I'm not saying they should make air moves impossible to use near the ground, I'm just saying that having to do an arbitrary cancel to make the move possible to use close to the ground is stupid when the option exists to just get rid of landing lag.
A lot of people disagree with l-canceling, even in the Smash community. However, I agree with it because to me it's the equivalent to learning how to link in Street Fighter 4 or really do any complex combo in any fighting game. You need to learn the timing of l-canceling by practicing just like learning the timing of links which also makes the possibility of "dropped combos" giving the chance for the defending player to punish.
The thing is that l-canceling timing differs depending on your attack, whether you whiff, land a successful hit, land on a hard shield (less lag), or land on a light shield (more lag) which adds to the complexity of how you need to react to the game. To be honest it kind of reminds me of the timing with pushblock guard canceling in this game because you need to practice the timing which differs depending on the properties of what the attacking player is throwing at you.
If I'm being completely honest I always felt shield cancels were always shallow and only served to get rid of any purpose landing lag had in 64 or Melee. That's one of the few exploits I don't mind Sakurai fixing in Brawl with auto-canceling.
L-canceling (or shield canceling as you incorrectly called it) is not a bug/exploit. It was intentionally programmed into the game. Wavedashing was also not a bug, but I would consider it an exploit since originally it was made to fulfill the case when a directional air dodge encounters the ground, not for mindgames, smoother movement (move to new positions to maintain combos and pressure/stage control/ledge control), and mid-attack reversals (wavedash out of shield). The metagame basically just took these mechanics to their limits to essentially create a completely different game that Sakurai didn't expect. It really shows how beautiful and elegant the game is because even after 12 years the community is still finding new things in the game even though the game doesn't even support patching! Even with this the game is still surprisingly relatively balanced, especially if you're looking around the top 8-10 characters.
Also auto-canceling is in Melee and Brawl. Not sure if it's in 64 though. I don't know what you mean by Sakurai solving l-canceling with a feature that's in both games?
but then everyone would just do a jumping move then grab you during hitstun/blockstun like in smash64
the l-cancle was an elegant solution but i guess he could just make landing lag shorter on the average
In Smash 64 l-canceling negates all landing lag, whereas in Melee it only cuts it in half. Even with 0 landing lag l-cancels in 64 shield grabs aren't that common unless you're playing with bad players since it's solved with good spacing and pokes. You just have to properly control your jump arcs so you either don't go too deep into their shield or just go for a crossup. If anything the 0 landing lag makes it harder to shield grab people, yet in Melee shieldgrabbing enemies isn't that common in the current metagame since everyone knows how to poke well or just play Fox and Falco where you can just shine to make most of your aerials relatively safe.