Disclaimer: I have hesitated to actually reply, but I have finally decided to challenge the question somewhat; or at least to bring alternative proposals to the table.
This answer will assume that all players, including the GM, are actually willing to play the same game.
If some players are only interested in bashing things without any real danger to their characters, others want gritty and dangerous and yet others want to emphasize role-play and creative solutions, then I am afraid there is nothing I can help with... A Frenzied Berserker and a Saint with Vow of Peace together do not go.
I have found it useful to be more explicit while composing the party.
By that I mean that most of the times I have witnessed parties being described by classes. While it may be useful, however, classes are ultimately building bricks and while they can give a general indication of the power/role of a character I have found it quite useful to have all involved discuss and agree on roles and personalities (*) (of characters) rather than just on classes.
While a Cleric is a powerful chassis, a Summoner, a Healer and a Divine Warrior are vastly different in their contributions to the party.
This matters all the more because... the power imbalance only really shows when there is competition! If both the Monk and Mighty Cleric compete to kill the same foes, the Monk may quickly be frustrated. Why? Because they compete.
As an example, my last born character is a very resilient martial character (based on Crusader) with non-negligible social skills:
- on social interactions, it could compete with the Sorcerer of the group, however I know the player well and we instead operate together; also, our characters have different interests and thus are not drawn to the same discussions/problems
- in melee, the GM knows I can soak up damages more than the Barbarian (lower AC) or Druid (lower HP); also my role is complementary, I immobilize, they kill (when the dices work)
My character is substantially more optimized than the rest of the party, which was a fun exercise for me, however it was optimized specifically to fill in a role with no competition in the party, and thus the other players do not mind as I do not inhibit they fun (on the contrary, the Sorcerer and Ranger actually appreciate it).
When characters do not compete, power imbalance may well disappear.
(*) For example, my group's Sorcerer is very reluctant to make any effort and is quite cowardly. As a result, unless really pressed for, the character will seek cover, sling a few pebbles or low-level spells from hiding, ... Thus while a Tier 1/2 in theory, in practice it does not steal the spotlight from anyone.
If the encounter ends in 3 rounds with only the Cleric really working at it, then the encounter is just not challenging for this party.
I am not saying that 3-5 rounds is not a typical duration for an encounter; it is... when the whole party kicks butts.
You might want to revise/adjust your encounters to challenge the party. It is a powerful party (3 Tier 1 characters after all), so bump the CR of encounters. Also, you might consider diversifying the foes; a mix of Big and Small allows more foes (making it less likely than a single character can handle them all) and a mix of Melee and Ranged (preferably inaccessible, or starting hidden, ...) allows more varied responses from the party (playing to different characters' strengths).
You might also look into dividing the party's attention: when divided, it loses in efficiency and has to use sub-optimal methods to solve its problems, allowing more characters to be able to jump in.
As you mentioned, the Monk (or Fighter) is just too far behind in terms of power compared to its 3 companions.
It is important I think to realize that classes are nothing more than bricks. You can play an arcane caster without playing a Wizard (and actually a Psion is kinda similar) and you can play an unarmed fighter without playing a Monk or Fighter.
Once acknowledged, this is freeing!
So, let's take the example of the Monk. Does the player want to play a monk (aka, lived in a temple) or does the player want to play a martial artist? Does he know about the Unarmed variant of the Swordsage? The Fist of the Forest class? Would he be opened to Changeling/Warshaper cheese?
And most importantly, does the player realize that apart from fighting/skulking a Monk does not contribute much... and skulking will be rare because the other players get bored during skulking panels (because they do not participate)?
This is why agreeing on the genre of the game and the roles in the party matter! Now you can show the player where/when its character will be able to contribute and where/when it'll be boring. If it's fine with the player; let's go! If it's not, it's time still to make some adjustments to the character so it can contribute (even if not shine) in some more areas. A level of Ranger could bring Track on the table...
Alright, so let's suppose we have a Changeling with levels in Swordsage/Warshaper; it's still not exactly on par with super-Cleric...
... but you may be able to close the gap by providing specific items in treasure drops to address vulnerabilities/gaps of the weakest characters. For example, what about the Gloves of the Unbalanced Hands or an Amulet of Dodge +3?
Of course, the other players need drops too; but not as often, and not as massively helpful. Also, they might want to buy very specific items anyway... oh, and you (as a GM) has your say on what they can and cannot buy.
Note: in essence, you may want to adjust the "Wealth by Level" based on the character's Tier. Multiplying the baseline by 1 + (Tier-1)/3 for example would allow less powerful characters to close the gap a bit by sheer equipment.
Note: these last two points address points specific to the OP's description of his group's actions and are less related to the core question.
I believe there was a comment about the Wizard and Druid not having sufficient time to buff...
When the party is ambushed, there is no time to prepare. You were sitting calmly around the campfire when a fireball explodes in the middle of the group, do you:
- Draw your mirror out of your backpack, assess the damage to your hair/eyebrows, attempt to minimize it, cast 3 buff spells to... ?
- Roll toward cover?
In a realistic setting, when the enemy has the initiative, it is unlikely to let you prepare yourself for the fight while it waits for your go (unless it's a Knight).
Actually, that is the very interest of ambushes; as a player, being the victim of an ambush forces you to play it up with an imperfect setup. And remembering how the Orc reacted when you faced it armed with fork in one hand and corn on the cob in the other makes for fun memories.
If some of your players have not understood that the characters will have no round or only 1 round to get ready to fight every so often, then it is time to make them confront reality. You may want to help them assessing exactly which short-term buffs/actions are absolutely necessary and which can be skipped in a hurry.
Finally, I am afraid that the Wizard and Druid will have to do their homework.
Druids sometimes take up so much time at the table - everyone reconfiguring stats depending on the type of creature they Wild Shaped into.
Wizards also take up so much time - often minutes flipping through pages of their spells deciding on what is best to cast.
Within my group, players are expected to announce their actions as soon as it is their turn. And they should announce their results swiftly. Not ready? It's assumed your character is hesitating and just defending itself (*).
In my case, playing an Initiator, I printed the Maneuver Cards; both useful for keeping track of which maneuvers I have available (ie, readied and granted) and to have a brief reminder of their effect in case I have a memory lapse. I also complemented the cards with Duel of Wills and Demoralize Opponent cards, because those are specific skill uses that I take advantage of so I want the rules at hand.
In the case of your Druid, this implies having the stats at hand for:
- their animal companion
- any creature they wish to summon, accounting for feats
- any Wild Shape form they wish to assume, accounting for their gear
They can prepare those on cards/character sheets as they see fit.
In the case of both your Druid and your Wizard, this implies preparing an executive summary of all the spells they wish to use. I would recommend small cards (like the Maneuver Cards), as it allows only having in front of the player the ones that can be played (ie, prepared and not cast yet) thereby reducing the choices.
If a player does not do its homework? Well, the character will gawk a lot... (**)
(*) Unless you are contributing to the group's well being by making sure the children stay put in bed or by bringing fresh drinks/food to the table, obviously.
(**) Newer players may have more difficulty. This means that (a) they should pick simpler characters (no Wizard for a beginner, sorry) and (b) the group should give them more time... but still a finite amount. I would suggest a melee character as it comes with the "Full Attack" default action.