Jaesun
what an RPG is changes along with the players of RPG because unlike other gaming genres the RPG is not a genre and it is more of a "template", a collation of systems whose relationship produces an unique experience that is not possible in any other gaming sub-genre.
personally when i was in my teens i thought an RPG was a game with a story and characters, then in my twenties i thought an RPG was a game with a story and characters and interactive "questing" (i.e. what the codex deems to be C&C), and now i consider an RPG to be any turn-based game whose gameplay is driven by strong numerical design and that features good encounter design, itemization and mechanical systems.
story and characters and quests no longer make the cut for me, but they still do for a large portion of RPG gamers and it's all fine: that's the entire point of our love for the RPG experience. it is simply not something simple enough to be defined as a genre.
since the RPG's themselves are made by the people who play them and are thus shaped by them it is a symbiotic relationship and it is much more dynamic than the same type of relationship between gamer and developer in other sub-genres such as racing, fighting, etc; precisely because the RPG is not tied down to any one specific overall presentation and is a template of design ideas born from table-top gaming in the 70's that is continually tried to be adapted to the video game medium in ever evolving ways.
EDIT: so to answer your indirect question Larian's first Divinity games are not RPGs to me because they are Diablo-clones in their combat model, but they are RPGs to others because of the much richer narrative, characters and the amount of depth in its systems. if i were asked to classify them objectively then yes, i would call them RPGs, but here among fellow RPG lovers there is less need to be objective.
to an outsider i would call them RPGs because they do not have any pre-conceived expectations firmly established over decades of playing RPGs; to someone who says he or she loves RPGs and asks me about them i would be explicit.