I guess i'll elaborate to explain why this further pushes bowser into the 'polarizing' category of characters.
So for rob to continue a lot of his combos, he has to jump super high into the air and go for a fair/upair or w/e. Bowser can simply react to this and nair, and rob can't do anything about it. Because of the way rob functions needing his jump/double jump to extend combos, as well as his floatiness, rob simply can't bait bowser into doing the nair. There are no visually ambiguous situations where i could make it seem like I was going to follow up, then wait out the nair, because any situation where ROB is close enough to follow up, if bowser Nair's he has no way to avoid it. This makes robs combos just not work 90% of the time on bowser.
Now compare this to falcon, or falco, or really any fast faller with a good combo/juggle game. They don't even care that the nair has armor, because they have enough combos that are so tight that bowser doesn't even have an opportunity to nair out for the trade, and in the juggle situations they have good enough ground speed to actually bait bowser into nairing and dashdance away for the punish, or good enough fastfalls to empty hop/empty jump, then fastfall to avoid the nair and punish.
By giving bowser a tool like this and expecting him to rely on it, he just becomes obnoxiously difficult to play against for 30% of the cast, and is literal trash vs the other 70%. Making characters with no even matchups, and only very good/horrible matchups is pretty clearly not something the DT is aiming for. Any logic you could use to support bowser having the combo breaker nair could also be used to support zelda's 3.02 nB, which, for those of you blessed enough to have never played against 3.02 zelda, was intangible and auto-canceled. Some characters just couldn't combo zelda, period, whereas other onese like roy/marth/falcon could just play as if the nair weren't there, which further pushed zelda into the 'polarized' category.
What bowser needs is ground tools good enough to justify his terrible combo weight. imo bowser should be mostly focused around edgeguarding, since that's his best aspect already. stuff like moves/throws with higher base knockback to better set up for earlier edgeguarding. not sure what in particular but you get the idea