One way to think about roleplaying is, roleplaying is the umbrella act. Each rpg offers its own take on this larger, transcendent act, the act of roleplaying. Some rpgs' rules get you (you in particular) into the act of roleplaying more quickly, more reliably, more soundly...
...And so it makes sense that you'd shop around, look for the rpg that gives you the roleplaying experience you prefer, try different approaches, seek your ideal, and (for some of us) create the game that gets you roleplaying just right.
Another way to think about roleplaying is, roleplaying is the small, technical act, just the act of roleplaying. Each rpg includes this act for its own technical reasons, in pursuit of its own specific goals...
...Just as a game might include the act of shuffling & dealing cards, passing turns to the left, or holding down B to run at top speed.
It might even be an absolutely central element of play, but it's there in its place to serve the game's design.
From this latter pov, the "ideal roleplaying experience" is a strange thought. It'd be like a game offering somebody their ideal card-shuffling experience or their ideal turn-taking experience.
Here's an example: I don't imagine that Murderous Ghosts offers anybody their "ideal roleplaying experience," but it's a fun game, worth playing on its own terms, and the technical act of roleplaying is essential to its gameplay.
Okay! You might guess that I personally favor the latter pov, and who cares. But I see two serious problems with the former pov that I'd like to highlight.
First is, D&D exploits the idea of the umbrella act to secure its position in the field.
Because of the long-standing equation of D&D = roleplaying, the idea that every given RPG is its own way into the umbrella act of roleplaying = every given RPG is its own way to play D&D.
Second is, different rpgs do, after all, have different goals. As these goals diverge, this creates a problem for the umbrella act. Our efforts to solve it have been divisive and poor: wrangling over "different kinds of rpgs," "rpgs vs storygames," and "that's not even an rpg!"
Looking at roleplaying as a technical feature of otherwise diverse games, I think, better shows the possible diversity of rpgs, and better places them in context with all the other games we play.
Many of Apocalypse World's rules refer explicitly to the interactions you have when you play.
Implicit: On a 10+, your character hits theirs. They choose where.
Explicit: On a 10+, tell them that your character hits theirs. Ask them where.
A lot of the time, it doesn't matter. The examples above are basically interchangeable.
But compare these:
Implicit: On a 10+, your character guesses what they should be on the lookout for.
Explicit: On a 10+, ask the GM: "What should my character be on the lookout for?"
These aren't interchangeable in the same way. In the implicit version, you have to kind of guess or interpret what interaction you should have with the GM, to get the result the rule describes. The explicit version describes the interaction directly instead.
Apocalypse World says "play to find out what happens."
What it means is, play to find out what the characters make of their world. Both what they choose to make of their world, and, because Apocalypse World is a game of compromises, what they're able to make of their world.
This appears, more or less explicitly, on the back cover of the game.
So you have a whole bunch of stuff in a game's design. Characters, fictional setting, dice, rules, abilities on character sheets, player roles like "player" and "GM"...
...And you have the moment of play, four friends talking together, live, right now.
It's tempting to say that the design-stuff "constrains" the moment of play, that the moment of play "enacts" the design-stuff. But I think that's backwards.
In the moment of play, you reach into the design-stuff and choose what of it you'll bring to bear. Better to say that the moment of play draws on the design-stuff, that the design-stuff is there as a resource for the playgroup to use.