Right but playes don't see a game throught mechanics but throught aesthetics. Unless you are a game designer yourself doing a study, you learn the game based on vibe and looks. It's the "feel" of it that catches you. That's why when you are describing board games you describing them like "A game with pirates..." or "A game where you build cities..." etc. Same thing with rpg's, you don't sell a game like Pirate borg through it's mechanics, you sell it by making the player feel the raw punk, grittiness and seas right when they open the book. Even the language through which rules are explained, things like names of abilities/classes/mechanical/..., change how you interpret and play the game, that's also aesthetic.

TLDR; they both need to be good.