First off, is l-cancelling an option? Nope! You will never want to not l-cancel, ever. Every other tech has reasons for not using it when the possibility is there, but not l-cancelling. There will never be a situation where you'd want to get extra lag on your aerials. The landing animation was already covered earlier, better options always exists over not l-cancelling, making it moot.
Secondly, what does proper l-cancelling teach you? Adjusting your button press for hitlag. That's it. Other tech do more then that. In order to properly use dash dancing, you need to be aware of your stage positioning, the opponent's effective range of attack, and, when tech chasing with it, be aware of the opponent's get up options (although this is more along the lines of tech chasing in general). For wavedashing, it's mostly the same thing, be aware of your opponent's range, your own positioning and what options you'd be able to use accounting for endlag and the gained distance. And the best part is, once you know what to look for to maximize DDing or wavedashing's effectiveness, the difficulty of doing so doesn't change, because at what ranges your opponent will be will change depending on your opponent's playstyle. Once you've mastered l-cancel timings, there's nothing there that teaches you anything and, worse, the "interactions" of the tech stop being there (it's between quotation marks because tech cause interactions by being used successfully, not by being failed).
Going off that, if auto l-cancelling would be tournament standard, what would be lost? At high level play, until proven otherwise by a certain someone with his
own evidence, l-cancels are not missed. And since I've shown that, once mastered, l-cancelling doesn't provide any interactions, the only thing that would be missed is the button press.
Now, if you want to argue about pressing a button being a sign of "true skill", then I'll refer to you to Rawkobo's post:
The post being replied to is
here.
I've presented my case. Again. And I'll eagerly await any counterpoints that are based upon sound logic. Hopefully not in vain, but considering the track record of the pro manual side, I'm not going to have any delusions.