Take that up with the designers of the game, I guess. I'm playing the game they designed and my arguments are based on the same.
No, this on you, not them.
Where is it written that never "RPing" to your own disadvantage makes one a "power-gamer?" Other than in your post which is just your opinion and full of pejorative labels and baseless insinuations.
Where is it written...?
Really?
That's what you want to go with? I'm not sure 5E D&D defines power-gaming at all, so I guess by that logic, nothing is power-gaming, nothing is being a munchkin, and so on.
And it's not baseless. You're hoist by your own petard, here. It's you who have suggested that you literally never RP in any way that you think will be to your disadvantage, that you always find a way that you could/should know/do something, never that you shouldn't. And that's obviously power-gaming.
Basically, your entire argument here boils down to rules-lawyering in the name of power-gaming.
That really is what you're doing here. Instead of taking accepted understandings, and realizing that the game isn't perfect (D&D 5E is much worse at explaining both RPing and DMing than a lot of other games, including 4E), you're trying to find loopholes, and failures in definitions to fly this 747-sized "stats mean nothing at all and can be 100% ignored for RP purposes" argument through. And to some extent you've succeeded (not in proving it's good RP or even RP at all, but that in proving it isn't specifically called out as bad, unlike other editions).
As for examples, I asked a number of specific questions - your response re: what games your in is the first time you've even come close to a specific answer, despite demanding examples from me re: bad behaviour (which you then ignored).
Anyway, I've said my part. You're rules-lawyering some stuff that's barely even rules, in order to find fig-leaf argument to hide blatant power-gaming behind. I don't think anyone else here thinks never RPing a character in a way which would intentionally put you at a disadvantage, is "good RP". My personal opinion, and this is obviously just that, is that's dishonourable, even unconscionable, to do that. I couldn't even begin to count the number of times I could have ignored my PC's personality/being and just said/done the smart thing, but didn't, because it wasn't in-character (and I didn't need "rewards" to do that, either, good grief).