The question has had a fair amount of significant information added since I wrote this answer, so I'm applying major revisions to make it more topical and useful.
The issue of disagreement over strategies and tactics, and how to advocate for one's own preferred approaches, is a pretty common one that I have experienced as a TTRPG player and observed as a DM. What follows is a list of considerations that I have found to be (or observed to be) effective:
1. State your case during planning, not afterwards
This was identified in a comment as an issue for you:
it's more of a situation of "group discusses "strategy A", you'd think "strategy B" might be better but since the majority's already on the plan A, trying to bring up "B" when people want the battle to continue makes the party frustrated with you for dragging your feet"
The rest of the players have settled on Strategy A, while you prefer Strategy B, but since other players have already chosen A, you feel that it only slows things down to advocate for B.
The natural question to ask is, what were you doing while the rest of the players settled on A? Even if it's a quick process ("let's do A, is everyone onboard?"), that is the appropriate time to discuss other options. Speaking out during the planning stage is being part of a discussion; not doing so cedes the opportunity to discuss, and following up with B seems indecisive at best.
2. Have a reason why your plan is better, and reasons why you don't like the other plan
I have tried to "be the contrarian" the few times this situation has happened, but it's been shot down pretty dismissively "just roll with it, it's not like you're gonna die", and then it turned out to be complete luck I didn't (Turns out those enemies have long-range weapons and I can get critted oops)
In a previous version of this answer, I argued that your party's approach is good enough, even if not optimal (by whatever definition) because you have been winning your combats. That's a pretty powerful counterargument against adopting your preferred strategies-- what is there to be gained from using approach B when approach A has a great track record?
Being contrarian is not, in itself, a goal that is usually worth pursuing. Being a contrarian implies that, regardless of the situation, you just want to reject the most popular opinion of the rest of the group. Your plan being different is not an argument in its favor. Your plan being better is such an argument.
Since your party hasn't been losing, you'll need to highlight what better results your preferred strategies will bring. Are you burning through healing potions more quickly than they can be replaced, trading sloppiness now for mortal peril later? Are your PCs using up spell slots too quickly, repairing damage that might have been avoided? Even if you don't have a better plan, you can and should talk with the other players about outcomes and consequences that you don't like and would prefer to find a way to avoid.
These sorts of considerations at least get everyone on the same page, and you can discuss the risks and benefits in a straightforward manner.
3. If already in combat and trying to change plans, recognize the mechanical limitations combat imposes and display confidence in your tactics
Battles in D&D 5e already are one of the bottlenecks in the game. Depending on your DM, they can take a really long time. The rules of the game also discourage table talk and pauses for reconsidering tactics. Mid-battle is too late to have much discussion about that sort of thing, and if your table enforces communications-per-turn rules it may not be feasible to do even if necessary. The ravening monsters won't sit back for a five minute break while your party confers, or even for the round necessary for each party member to participate in a six second conversation.
Instead of trying to pause combat to have an orderly debate about tactics which you bring to a consensus, it may be better to shout an utterance if possible ("they're swarming through the tunnel, fall back to cover!"), and then do what you feel needs to be done. Your party members will almost certainly respond in ways that account for your new, off-original-plan action. If your plans are so good as to be optimal then they shouldn't cause combat to collapse into a TPK. Either way, you can talk with your party later, when there is time for discussion, about things.
4. Understand what you're optimizing for
But I would be lying if it didn't frustrate me be made to do less than ideal things
As above, it's not clear to me in what ways your party is worse off for using the strategies you describe as sub-optimal. Consequently it's worth talking about what you mean by "optimal". Optimizing for time (in the sense of finishing combat in the fewest possible rounds) might suggest very different strategies than optimizing for damage taken (you want to maximize your conditional AC and full cover options, for example), which in turn may be very different from optimizing for spell slot use (avoiding using non-cantrip spells as much as possible in combat).
There are many situations which will be suboptimal, if solved as an equation on paper, but will not have any practical effect. For example, if a druid is already going to use Wild Shape anyways it may make sense for them to tank damage as well, and so may not fit in well with a damage-minimization approach (as you get the beast form's HP for free, with no benefits for keeping it high).
Additionally, it is relatively rare in my experience for a tactical choice to be strongly dominant over all other choices in all cases. So it's worth being thoughtful about whether or not your preference truly is optimal in a way that you can define and defend, and also whether or not "suboptimal" play is likely to make a material difference in the game. It is uncommon that truly optimal play is necessary to keep from losing the game (whatever that means in a given campaign), and so an argument that a strategy isn't optimal may not have the weight you expect.
5. Double-check that you, the other players, and the DM are on the same page about the challenge of the campaign
the campaign we're playing is generally seen as difficult.
Regardless of the campaign you're playing, your DM may be lenient or punishing. If your DM makes efforts to avoid risk of TPKs, then optimal play might just not be worth pursuing because the level of risk doesn't demand it.
This sort of thing happens all the time. Some tables are very strict about carrying capacities and item weight, and so have a need to optimize for those. Other tables ignore weight and carrying capacity altogether, and at such a table trying to get players to be careful about those elements really would be a waste of time. It's worth asking your DM if the level of optimality you want to bring to the game is needed, or if it fits at all.
6. Trying to have fun at the table is not a waste of time
Finally, a high-level consideration: presumably, you're playing D&D to have fun, and if you're not having fun that is a valid concern to bring to the table. It may not matter if you choose strategy A or strategy B in a given combat, as you'll win either way, but it matters if A is not fun for you while B would be.
The approach you choose, in-character or out-of-character, is less important than pursuing what you actually want. You are clearly willing to make compromises in service of the other players having fun, and it is not unreasonable to expect them to do the same at least some of the time. Even if you have trouble with my other suggestions, or others in other answers to this question, you shouldn't feel guilty about telling the rest of your table when situations erode your fun.