I've bolded a key word in your post.I would guess that, in dnd, acquiring more power (as usual) but making suboptimal decisions counts as capital-R Roleplaying.
Suboptimal only becomes apposite in a context where the goal is already established, and the decision is counter-productive in terms of achieving it.
Even then, there are complexities: for instance, in Gygax-ish D&D if the best way to get the loot is to drive all the dungeon inhabitants out with a Cloudkill spell; but I object to that because I'm playing my paladin as upright and honourable; then I'm making a suboptimal decision - or maybe not? After all, alignment and similar restrictions are part-and-parcel of the parameters of the game, as much as the XP rules, and so by ensuring I don't suffer any penalties from violating those constraints is in fact sensible and perhaps optimal play.
But let's think about something more interesting. Is pursuing my drug habit - which enhances my magic - to the extent that it ruins me financially and results in me losing my house, suboptimal decision-making? From the point of view of the character, probably - his life went down the toilet, at least for a little while. But from the point of view of the player? When this happened in one of my Rolemaster games, the player was deeply invested in the whole thing, and played out his character's fall (which included agreeing to betray his city in return for a magistracy and the return of his house), and redemption through love, and then a different fall after his lover was killed by a summoned demon that went rogue.
If the goal of play is to find out what happens to my character, then there probably are no "suboptimal decisions" in the sense that phrase is used by D&D players, because whatever decision I make, I'm finding out what happens to my character.