My responses to your comparisons with other fighting games are under a spoiler tag to not detract from the main topic. I honestly don't feel like continuing that part of the argument because it doesn't add much to the discussion in this thread.
It was deemed "broken" enough to be removed from the game. Don't see how less laggy aerials across the board would make the game worse as drastically as you make it sound here since 64 turned out pretty decent with completely lag free aerials (especially when l-canceling had a massive window), huge shield stun and very weak DI... but whatever.
You'd still have the low hitstun (and canceling), the floaty physics, the bugs, etc... Would it have made Brawl a bit more exciting? Perhaps. But it would still be a pretty bad game compared to its predecessor because of everything else.
And that's why we're having this discussion. There's plenty of possible ways to achieve balance; look at frame data, figure out what could (and should) be punishable on reaction, an appropriate punish window, etc...
Maybe my comment about l-canceling in the OP was a bit harsh, so I'll just elaborate on my attitude a bit;
At the end of the day, here's what the situation is looking like right now: Sakurai and his team have made a conscious effort to remove L-canceling from Brawl and unless his design philosophy makes a complete 180, it's safe to assume that the mechanic as we know it will not be returning in future installments. I'd love to eat crow on this, but even a huge community effort wouldn't make Ninty change their mind. So at some point its time to move on, and try to figure out a way to retain the positive aspects of l-canceling (combos, defense) while staying compatible with Sakurai's vision (regardless of what we think of it).
If the choice is between another Brawl and a slightly more newbie friendly, albeit less technical Melee, I'll take the second option every single time (and I'm not sure how anyone could argue otherwise). That's all.