Wavedashing is useful, just figure out a more "ergonomical" (for lack of better word) way to execute it.
As for L-Cancelling, that's just bad game design. A mechanic that you want to do 100% of the time with no drawbacks at all? Take that out. Just half everyone's landing lag. At what point do you ever want more landing lag?
And before someone brings up something about how L-Cancel is like basketball, no it's not. Not even close.
There's no point in Wavedash if it isn't balanced and requires no effort. It doesn't work as a button press either. It's specifically designed in a way that requires you to actually properly direct your character during a jump while pressing the Shield button. The issue has always been the input commands, but it doesn't work any other real way. The best they can do is still force you to properly aim it with the control stick, but have a button that activates it if you're decently close enough to the ground. It'd make it easier to do, without taking away its usage, which is viably moving around faster and dodging some attacks. It's much harder to simply as a move as you're saying.
No, L-Cancelling stays because that's key to how Melee is designed. Yes, it is badly designed. But it's still a core part of the gameplay that made it notable. There's no reason to remove a legitimate and super easy to use tech when problemsome glitches exist and deserve removal ten times more. The thing about it is that it also helped with balance because it did allow more in-depth gameplay in the long run(no question that it was done in a shallow way, but the results still show that it created more depth. You can't do that with auto-cancelling in any way. Not the way it's been implemented, anyway. See a lower paragraph for a thoughtful way to do lag cancelling that is both balanced and isn't poorly implemented).
The landing lag should never ever be halved for everything. It should either require effort to do so(minimal even) or should be based upon the move, for balancing purposes. Simple solutions like that are half-assing the balance entirely. You might as well not have any change to landing lag. If it's the same for every move, it does nothing at all. Characters need to be properly looked into, and lag should not be removed for all moves. It's the only way to really balance it well. Which is a pretty big failure in every Smash game unfortunately. While there are a lot of moves, having some with lag can justify how strong or hard to dodge they are. There's legit balance this way. This is the only good and proper way to do it with L-Cancelling gone.
And to be honest, completely removing what makes Melee even playable just ruins the game. It's better to not remake it than to remove the two core mechanics that made it even worthwhile in competitive play. Overhauling them in a balanced way is fine, as long as they still work in a way that keeps the original game's design. This is the reason a lot of remakes are panned. It completely messes with the original game way too much. FFVr's new battle system can be a huge issue for those trying to enjoy an improved version of the original game, for example. Some don't mind that battle system, but nostalgic players want the Gauge Battle System back. It was also a fairly balanced one anyway.
...Who actually compares L-Cancelling to basketball? Nobody is arguing it's unbalanced. It's just taking it away completely takes away what made Melee even remotely popular to play. Which does not bode well for trying to sell it to players who want it in HD or with more balance. It's a better case of "just release it on the VC without messing with the game". It's still a damn popular competitive game to this day anyway. That hasn't changed, and more than likely never will.