Problems with the Monty Haul campaign
Back when Monty Hall was the host of Let's Make a Deal TV game show, folks used to call what you’re describing a Monty Haul Campaign. (Get it, like “treasure haul”?) Like contestants on the show, characters in the campaign get fabulous treasure just for showing up.
Some DMs try to make their campaigns different by handing out treasure not seen in more typical campaigns. You and your fellow players feel there’s something not right about that. Don’t let anyone tell you that your concerns are not valid.
Breaking the game economy
Scrimping together treasure to afford the next item on the shopping list is part of the game. If the party gets practically limitless cash early on, they can just buy anything that’s available. Buying equipment loses its thrill.
Magic Items and Great Treasure as Railroading
Easy wealth wasn’t a story you or the other players wanted, but the DM pushed it on you. That’s really a kind of railroading.
A central part of the fun of D&D is the shared storytelling. Part of any D&D campaign is character advancement, and treasure accumulation is part of that. “We fought some goblins and became fantastically wealthy,” isn’t much of a character story.
Overly powerful items that just turn up can reduce player agency, down to every die roll in combat. If some overpowered, exotic weapon appears in a treasure horde, then the party is kind of obliged to use it. The players might not feel this weapon is as cool as the DM felt it was.
Consider the typical +1 dagger that a party may find early in the campaign. There’s a discussion of who gets it: it might be the mage (who uses a dagger already), the dual-wielding rogue (who might use it instead of one of his short swords), or the fighter (who will probably be standing in front of whatever monster, when the party discovers it resists normal weapon damage). Any of those choices might be best, depending on the play styles involved. The party won’t be hugely better off one way or the other. That’s how it should be.
A +4 longsword is a different matter. Assuming the DM re-balances encounters to factor in the weapon, the choice for the party may become “use this weapon or die.”
Acquiring powerful items and great treasure should involve choices made by the players. If you never sought to become rich or learn amazing secrets, these things shouldn’t fall into your lap.
A DM can make it possible to find great treasure during any campaign, for instance by slaying a dragon that is ancillary to the main plot. And a fantastic “vorpal gizmo” beyond normally available weapons could require research, a feat, or some other action to utilize it.
Powerful magic items can make character building less relevant. At its worst, the PCs become just the folks that carry around the DM’s awesome magic arsenal. (That’s nice your wizard learned to cast fireball, but she probably should keep using her Staff of Unlimited Meteor Swarm.)
Fixing OP items without retcons
Your DM seems at least a little receptive to balancing the treasure, but reluctant to retcon them out of existence. Here are just a couple examples of how to get out of that bind (bearing in mind you are in the middle of a PoE campaign).
That +4 longsword might belong to a deity or other creature who needs it returned to defend the heavens from some enemy. Or it might need to be plunged into some evil artifact, destroying both items. Overpowered but temporary items can be cool, as PCs struggle with the desire to keep the item.
A vorpal gizmo could turn out to be fragile. The wielder notices a crack that worsens every time (for example) the attack roll is a 1. Then the player has agency to use the item when he or she sees fit.
As for large monetary treasure, that’s easy. The party might be presented with some worthy cause that requires treasure, such as evacuating a population from some sinking island.
Should you just ignore this because the DM is otherwise so good?
The DM is trying to please the players with lots of cool treasure, but the players just think it’s too much. They feel the rewards are unearned so receiving them isn’t rewarding.
If the players do not address this, there will be a lingering dissatisfaction. How will the DM address this malaise? There’s a good chance he’ll try handing out greater treasure. The cycle would then continue until players start to conclude the game is just ridiculous and want to stop.
(That is what happened in the last Monty Haul campaign I was in. It was sad because the guy showed real promise as a new DM, and I’m not sure he ever gave it another try.)