first - once you apply presumption of an almost mindless blind obsession to a player type - the argument loses any significance at all. What about the roleplayer who only ever thinks of the romance angles and never even tries to take up any combat skills? What about the rogue who only ever wants to steal and never fights and so does not adventure with the... etc etc etc boring boring boring extremist dichotomies.
That *can* be disruptive! Especially if it's coming at the expense of other people's fun at the table.
Disruptive behaviour is disruptive behaviour.
Power gaming is the only one that gets a pass. It's the one people try and justify and make excuses for. It's the one that keeps coming up and people debate. I've NEVER seen a thread on a DM having problems with someone power roleplaying and overacting to the detriment of the party.
Because we all already know how to handle the guy that does something stupid and declares "But it's what my character would do." The DM just rolls their eyes and says "Rocks fall. Your character dies. Now roll one that isn't an assclown." No debate is needed.
But when the detrimental player is doing so via RAW, suddenly there's a question….
"It's not fun for the other people at the table if everything is dead before they get a turn. " that is a sign of a GM problem, not a player problem. the Gm creates and devises the adversaries and challenges and if he puts "fights" that are over that quickly often enough in play to be a problem for the enjoyment of others he needs to rethink his design and approach. i won't say i have never seen a one shot kill, because obviously it has happened but it was not as much a case of awesome powergamer fu as a lucky hit and a very weak adversary that was not intended to be a challenge anyway.
Kinda. To some extent.
The DM does need to account for their party. And a *good* DM will know all the strengths and weaknesses of their party and be able to devise tactics to counter and challenge them.
But that's advanced DMing. That takes system mastery not every DM possesses.
You're effectively blaming the DM for not being as good a power gamer as their players. And, of course, there are always more players than the DM with a much higher collective intelligence. To say nothing of online builds and the like. The DM will seldomwin that particular arm's race.
Example: I have a five man table. Average party level 8.
I need an encounter that will challenge them. Go!
But that's an unfair challenge. You can't. There's too many variables.
But even knowing the classes and races and magic items it is tricky. Because how many are power gamers? 1? 2? All 5?
Even as their DM I don't always know. Because the players are better optimizers than I am. They keep their bag of tricks close to their chest until needed.
A power gamer only has to worry about one thing: their character. The DM has to worry about multiple characters, multiple encounters, the overall plot, NPCs, and so much more. There's only so much time.
As for having one or more optimizers making it harder for the Gm to balance encounters - not in my experience. I have never found it to be that case that i did not have to put some work into balancing encounters and challenges - again - i see balance in play as the intersection of capability and need (key and lock) and so i factor in the character's capabilities most all the time.
Not having personally encountered a problem doesn't mean it doesn't exist for others.
The problem is power gaming increases the workload. It changes the balance of the encounter from the default presented in the rules and the default assumed by adventures. Suddenly, running a published adventure is harder because you need to reevaluate every single encounter to account for that one person.
To say nothing of having to "cheat" by increasing monster hit points and the like.
Using higher CR monsters is problematic because their damage output and special abilities are more deadly. A solution is to throw more monsters at the players. But then that also gives out more experience, increasing the rate players gain levels.
So the DM has to potentially "cheat' twice, increasing the challenge of fights and reducing the rewards just to "balance" things with one player.
As for your linkage of player performance vs GM favoritism... a GM intentionally and consistently giving one player more/better/cooler rewards than the others to the detriment of the game experience for the others that would be unfair **regardless** of whether or not it made them better in combat. its not that the rewards made them better but that the Gm was not treating each player as equally as they expect. it wouldn't be Ok if the "supper cool more than you" was all cash and titles and interactions.
That has nothing at all to do with what the players themselves choose to do with their options as given and the benefits they reap. there is no promise of "equal outcomes" implied anywhere by a GM - though there is a strong goal of equality of opportunities. Again that notion of balance being capability-meet-challenge applies just as well to capability-meets-opportunity. Gm hopefully runs a game where the choices and capabilities the PCs have get "equal enough" opportunities and challenges so that everyone feels engaged and useful. its not particularly hard if the Gm pays attention at chargen and backstory and just simply keeps at it.
If one player is simply better than the others, why does it matter what the source is?
If DM favourtism is bad, then so is the same result at the table from one player finding a broken combination or min/maxing a character.