Bowser's design is hugely, unnecessarily polarizing due to his being 'MURICA sized, his dependence on the armor mechanic (and a few very centralizing moves - nair, fair, dash attack), and his lack of available counterplay against dash dancing and grabs (notably, no means of hindering or discouraging dashdancing such as a projectile or low-commitment neutral options, and no remotely usable spotdodge), which collectively render him incredibly frustrating to crack for some characters, and a complete joke for others - hinging mostly on
1. how good the other character's grab game/followups are
2. whether or not it's a fast faller
3. whether or not the other character has moves with extreme rewards for precision (such as Zelda's kicks, the Knee, Ivy's upB, etc) that aren't actually remotely difficult to land on Bowser.
Bowser's still in a better state than he's ever been, but this stuff should be pretty straightforward to fix without making Bowser too strong.