You are comparing apples to oranges. Semantic HTML is important because it is a publicly defined semantics and various consumers and user agents are programmed

You are comparing apples to oranges. Semantic HTML is important because it is a publicly defined semantics and various consumers and user agents are programmed against this semantics. Semantics in class-names, the choice of inline styles vs style sheet etc. are purely for maintainability, e.g. you don't reduce accessibility for anybody if don't use semantic class names, at worst you make it more difficult for yourself, but that might depend on your workflow etc.