Enlighten me, then. How is a new game that, other than being of the same series with the same characters, will Brawl be less competitive due to the lack of the previous game's ATs? That's like saying Alpha 3, CvS2, and 3S aren't as deep of games as ST because the games don't play the same as ST.
I must reiterate what you're calling Advanced Techs are merely glitches that could be abused. In some cases, glitches become functions in future titles (such as 2-in-1s from SF2:WW becoming expected in fighting games today) if they prove vital to the game's future. As of now, we see nothing that proves that a future without techniques such as shield canceling and wavedashing were vital to the game's future. Wavedashing merely assisted characters, and really didn't add that much to the game other than speeding up the process. It made no sways in the tiers, it wasn't a revolution in the genre akin to functions like combos.
Shield canceling was only mandatory due to the functions of the block throw being too overpowering otherwise. So far, we don't exactly hear much about that crazy block throwing dominator out there, do we? Who's to say the lack of this function will put characters at enough of a disadvantage to make aerials useless? Again: it wasn't a revolution to the genre. It may have made the game deeper, but it wasn't because Melee wasn't already deep. It really wasn't.
Before the ATs, the game was pretty simplistic, and really had no depth whatsoever. The same couple of characters dominated the rest, and that was it. But that's the evolution of a fighter. People discover what is necessary to further the game's depth, if possible. You move onto a new game? New things to discover. Can't expect every game to have the same basic functions you just spent time on, only with more. A good example: Alpha 2 vs. Alpha 3. This is continually debated, as a big mechanic of the game, which took great skill to pull off correctly, was greatly changed almost to the point of being unrecognizably different. Custom Combos of A2 allowed you to continuously link attack after attack for a limited duration of the meter. To really get everything you could out of it, it took a lot of practice. People spent a long time to master this ability, as it was a big function in the game. Then Alpha 3 came out, and did away with the current Custom Combo system and replaced it with V-Ism, a remotely similar, limited time, massive combo building setup. However, rather that removing attack lag, one had activated time-delayed shadows that would continue the combo long enough for you to repeat it yourself. The change was so drastic that the entire concept had to be pretty much learned from scratch. Did this ruin Alpha 3? No. In fact, the debate still rages on on which of the two games are better.
Note that while my above example wasn't from a function that wasn't intended like the glitches we're talking about today, the principle behind it remains. Even drastic alterations to gameplay do not automatically destroy a game's potential to rival its predecessor. The fate of Brawl's competitive play is far too soon to call. It could be better than Melee. It could be worse than Melee. But in the end, it's Brawl, not Melee.