Video games do have genres -- RPG, FPS, action, adventure games, puzzle games, sports game, tactical wargames, sims etc. and their hybrids, e.g., action RPG or action-adventure. The difference is in gameplay. As a consumer, I want to know what I am buying. If I want a graphic adventure game, I want to make sure it is a graphic adventure game, not a FPS -- we share the same opinion it seems. However, have you ever seen "dungeon-crawler" or "story-driven" printed on a game box? Is "story-driven" the best description of Baldur's Gate 2 one is able to come up with? Is "sand-box" a fitting description of Fallout?
Following the same logic we can define RPG genres as RT and TB or JRPG, ARPG and ERPG to scratch our personal itch. Or Diablo-likes, Fallout-likes, Oblivion-likes. Also, Bethesda-likes, BioWare-likes, Troika-likes. Or fantasy, space opera, alternative history, western. Or grimdark and rainbowpony.
All this is equally informative when describing a game.
Let me repeat myself: the loose definitions (RPG, strategy, action, adventure) serve as guidelines when you make your purchasing decision. Further differentiation is artificial and serves no real purpose.
If you think there is one, please spell it out for me.
If nothing else further differentiation serves as a more accurate guidline for purchasing decisions. Especially in a genre like RPGs where just about the only thing all the games have in common is that the main character levels up one way or another.