Uh no, that's not true. I used this technique to help me beat a lot of good players. Mango tried to rest me once because he thought I missed my L cancel but I spaced it so my shield would come out before he could. I do this kind of stuff, it is legit strategy. Ask anyone who played Melee and even Brawl with me about my bait game. Of course this can't be your only strategy but you said it yourself, it gives you an OPTION. And let me reiterate, the bait game is much more viable in teams than it is in singles. You can DEFINITELY rely on "opponents being bad" in teams because they are distracted by 2 other players on the field, you can beat people make way more mistakes and have less time to think it through.
Someone else also brought up that there are ways to mess people's L cancels up, like powershielding, so this gives opponents multiple options to combat your strategy and envoke extra strategies on the opponents parts. If the L cancel was automatic, someone powershielding wouldn't mess them up, therefore the opponent would have one less option to fight back. (Again, i emphasize the word MORE OPTIONS). There is a lot of strategy, thought and options that result because of L canceling.
Hey Mr C - thanks for the kind words man. Hope you have been well! The new smash game has got me excited so I've been posting here again after years away