the thing about all the ATs is they aren't necessarily immediately vital to the game being playable at high level. The ATs may not exist, but that didn't stop us from playing the game in tournaments before they were even discovered. The only theoretically gamebreaking AT would be shield canceling, and that's only if the game behaves like SSB64 did before shield canceling, in where aerials were dangerous to use almost to the point of uselessness due to the overpowering tactic of block throwing. Shield canceling came in and made block throwing dangerous and unlocked the aerial game again.
This is not to say that the absence of shield canceling will break Brawl. From what it sounds like so far, top tier is BOWSER, and Bowser hasn't changed much, save super armor. If this were Melee, Bowser w/o shield canceling would be even worse off than w/ them. If this is the case, why are they considering Bowser a dominator? 'cause this isn't Melee. Different game, different rules, different experience. To treat this game as Melee 2 is to be ignorant from the start.
Who's to say that this game's gonna be glitch-free, too? Who knows if a year down the road, someone finds out how to make something tricky happen w/ the new air dodge that shifts the game around completely? That's how fighters ARE. You discover a tactic, that tactic owns everything. People start doing it. Then people start trying to beat it, usually discovering a new tactic in the process. The whole concept is cyclical until the game has been explored to its every orifice, finding every last inch of depth in the process. Only at the end of this chain do you find out whether a game is truly unplayable at high level. Hell, even at the end of the chain, someone may eventually discover a new link and expand on the gameplay even further. The only thing necessary is the willingness to try and find out what is out there.