thats what I've been advocating. Sure, we can name numerous numerous numerous players who are exceptions.
But oftentimes slow players with major league skills....usually big power....at some point get so slow that they can no longer field their position at all, and they clog up the basebaths. If they can find the AL, they are relegated to be DH, or maybe DH/1b. Although they still clog up the basepaths.
Players with above averge speed also become slower with age, but they are still at a level where they can actually play defense, and they dont clog the basebaths. And often, as they mature, they lose some speed skills, but gain power skills.