I don't think that giving Bowser super armor is necessary, though higher priority on his slowest attacks would help since if you get hit by them, you deserve to be punished for it. And change D-Smash from being a immobile Fortress with more knockback and damage to something better, like a powerful ground stomp with a significant shockwave around him.
I would LOVE for Bowser to have Charizard's Dsmash (which is basically exactly what you're describing here).
I have a very aggressive playstyle, but I know there are other approaches I need to learn for Bowser. If my aggressive playstyle does not work, then I adapt a defensive playstyle or even a campy slow playstyle if I am in the lead against another campy player. I've learned ways to adjust. My 41% win rate is due to me not being very good at Smash to begin with; I only started playing seriously with Smash 3DS. I played Melee and brawl very casually. My 41% win rate is also due to me learning the ways with Bowser. He is a high-risk character to use, but he can destroy people if you play him right.
The concern I have is that players are figuring out that the best way to play against Bowser is to simply wait for him to approach, even for characters without a projectile. The danger here is that, once everyone has caught onto this, it's going to be a game of "Anticipate which approach Bowser will use" and there are a number of ways they can do that without making enough of a commitment to punish.
What I'd like to see is a windbox on Dair and aerial Bomb (landing). Right now, it's insanely easy to punish these attacks to the point that no sane player would attempt to use them. It feels like a SH FB with good spacing is still a surprisingly good option because it doesn't make much of a commitment but still allows Bowser to go on the offensive.
Also, I WISH they had given him the "Tap B" to fireball and "Hold B" as standard FB as the default setup. Bowser being able to apply projectile pressure of his own (even if the range isn't amazing) would keep him from slipping down the tiers as well as give him some much needed options in the heat of battle...
Also, please don't mistake my concerns for unwarranted negativity. With a few tweaks, Bowser could be a VERY high tier.
BTW, do we know if folks from Namco read these forums? Smashboards is the largest SSB community in the world, last I checked, so it would make sense that they read it on occasion to get a feel for what people are thinking, right?