I'm with everyone else, really - as soon as 1.1.3 rolled around, I was one of the few people most hyped for Bowser's new throw options, but they're hardly spammable. I actually find myself jab-confirming them more than anything, and since you can shield jabs, well... A lot of Bowser's grab confirms are about mix-ups or catching your opponent off guard, and that's pretty difficult to do as a character who is so unwieldy as Bowser - and it's not like Bowser hasn't always been notoriously powerful against shields or had powerful options anyway. With options like Bowser Bomb and Klaw, the U-throw combos only really strengthened his vs. shield game (and kind of his rush-in game, which is non-existent anyway), which while it's a worthwhile buff, I don't think it adds anything particularly tactically powerful to Bowser's arsenal, it just strengthens him in a kind of power-creep way, which is actually pretty fair to me as it really adds to his Powerhouse status.
-and just by looking at the characters you play as, you shouldn't have any trouble spacing Bowser, or comboing him, for that matter. Dark Pit especially is really good at beating Bowser's approaching options, so you can generally catch him off guard with an early dash attack, or pressure him into bad approaches with arrows, dashes (again, the Pits' dashes are super good), your own grabs, short-hop F-air, and in the case he jumps, JC U-smash.
I think the key to fighting Bowser is to make sure he never succeeds in landing safely, because otherwise, he has basically no options. It will require some reading sometimes, and Bowser does have the option to just powershield through a lot of things instead of jumping, but that requires skill, and again, his attacks are pretty slow, and the ones that aren't have either horrendous end-lag, or just aren't fast enough.
As someone who plays Dark Pit and Bowser, I can easily say that the match-up is pretty even at worst for you. You're much safer than he is, faster than he is (attack wise, that is, do not try and run from Bowser if you're gonna go more than half the stage, since he can catch up to you as Dark Pit), and you have some pretty good pressure and (especially since Dark Pit got his Electroshock buff) some pretty incredible punishes. You just have to make sure to be a lot more patient around Bowser now, because one slip up and you can be dead in a matter of seconds (Which could actually be said for Dark Pit since 1.1.3, too since Electroshock has the potential kill Bowser at 90%.).
I can understand your frustration, but a lot of Bowser's power comes from his ability to make mince-meat of poor defences or panicked players if he gets close, and you shouldn't have any problems with Bowser's range or approaches at all. I actually find myself backing up a lot as Bowser if I'm being pressured, because there's just no way I can safely make use of my air tools, and approaching on ground is really damn punishable.
If anything, U-throw isn't that incredible other than for raw damage or KO purposes. His scariest tool is - and always will be - Fortress, since it's so fast for any other move Bowser can pull off and lingers long enough to punish rolls, which are the one thing that will get you out of the way of his stronger options, like the new U-throw.
The best advice I can give you is that... Bowser is still slow, and his air game still sucks so hard it makes Mac look average (Except his offstage. Do not underestimate Bowser's offstage.). Utilise that. Just don't stand your ground against Bowser, because his ground to ground game is pretty devastating in the right hands, it's kind of that simple, honestly.
