I've seen questions similar to this since 3e, and my response is always the same.
D&D simply isn't modular like this. As others have pointed out, the classes are not constant. Feats also have value that varies due to many factors (level, balance with other feats, etc). You cannot simply trade mechanics and expect the game to still fit together.
D&D simply isn't modular like this. As others have pointed out, the classes are not constant. Feats also have value that varies due to many factors (level, balance with other feats, etc). You cannot simply trade mechanics and expect the game to still fit together.