In the training options of the 20XX debug menu, you can turn on color cues to see whether you've executed a successful L cancel or not. White being successful, red being unsuccessful. This will help you see how consistent you are with L canceling. I'm pretty sure top players rarely ever miss an L-Cancel because how often they do it. I have been playing competitively for about two years now and I rarely miss my l-cancels, even with characters I do not play as. If you're having trouble executing l-cancels facing CPU opponents,try and do it in training mode or with a controller plugged in, do not use it in play until you are consistent with it, and then slowly bring it into play.
The method of training you're using (not allowing l-canceling on hard press) I personally don't think is required, because I mostly hard press to l-cancel and usually get it every time, and I learned through the vanilla version of the game. But I could imagine it would be beneficial, it would be quicker to lightly press the L button as opposed to hard pressing it, but not enough to effect your play.
Once you have the technique down, it is really easy to do.
