WoW and KoA both have cartoony art styles yet KoA doesn't touch the level of cartoony that WoW does, yet they are both high fantasy.
LotR and D&D are also high fantasy and I dare say KoA's magic system better fits to how D&D works.
Final Fantasy, also high fantasy, but doesn't go anywhere near WoW's super cartoon graphics.
Art matters visually. Gameplay is what matters. Gameplay and narrative direct art, not the other way around.
WoW, Final Fantasy, and LOTR are three VERY different styles of fantasy as far as i'm concerned. I don't care if you can technically lump them together under the high fantasy catagory - they're wildly different.
You're right that gameplay is what matters
as far as the quality of the game goes, but art dictates the overall look and vibe of the game, which is important too. At least to me. I love the TES style, not the WoW style, or the Final Fantasy style. If you strip all the artwork out of Oblivion and make it look like Final Fantasy, even if the gameplay remains identically the same, to me that would COMPLETELY change the game. It would no longer be TES-style Tolkien-esque fantasy. It would be Japanese anime-style fantasy.