If he had the ability to move quickly horizontally without finding himself in a bad position afterwards, my opinion would be moot and completely null... But most of what you'll see, if you're on the other side of a stage and Bowser's moving towards you, any of the 3 attempts (walking, running and jumping) would be easy to see where you're directing your character to go to. His attacks are fast which really helps create the illusion that he's a fast character, but his movement speed (even while on the top third in one of the categories) doesn't help his attack speed in any way. Other slower characters have attacks that may be slower/faster, but can be used at a faster rate, further proving that the character is a fast character, and not just one that is considered fast because of attacks' startup frames only.His movement speed is NOT bad in comparison to other characters. He's in the top half in running speed, and top third in air speed. How can that be considered bad?
Compare Bowser to other characters' approaches, and you'll find that his approach is slower than other characters... Many other characters... And I think I've used Bowser for enough time to at least have a voiced opinion, as well as seen a number of top-playing Boswer vids (I gotta admit, my favorites by far are the Bowser challenges... I love the sideB chains).