The problem with defining RP Gs
seem to be that the classical definition (player is playing a role) is not applicable anymore. FPS are also the player playing a role, like Gordon Freeman in Half-Life
So for computer games I would say the defining features are:
1) The ability to create and develop a character
2) Concentration on the character, not the player.
3) A strong element of storytelling...
4) ...which the character can influence by decision making.
How those are executed can theoretically vary very widely. Practically, there are common executions (for example "character skills over player skills" to satisfy point 2).
Stat-grinding and the like is not in itself necessary, hence. However, it serves to fulfil points 1 and 2.
And those elements do get too diluted these days due to "streamlining". I wonder what the hell is up with that - I mean, I can see why some
companies would do that to open up new niches, but it seems these days every-fucking-body does so, leaving the niche for "full, true" RP Gs