Z-cancelling adds a challenge, and that's why I like it. We've beat this horse dead into the ground a million times before, so to each his own. I'm just saying that I like that extra element of skill it adds to the game. It's nothing over the top or ridiculous and actually makes sense in the grand scheme of things. Pressing ABAA to do a jab just makes no sense. If I fall IRL, I'm going to put out a hand to recover quicker. Same applies to Smash.
The converse of your argument also applies, ballin. If I'm playing a standard fighting game, shouldn't the combos be much easier to perform? If I wanted to perform a hadouken, simply pressing A instead of a whole mess of buttons is so much easier, so why don't they do that? They should just make the best combos mapped to single buttons since I really don't want to learn the button combinations and strict timing and just want to improve at other aspects of the game.
Cancelling is Smash's way of making the game more like your standard fighting game. Many moves that have multiple hits, like drills, require fewer button presses than hits. Pressing Z in between attacks keeps the button combinations going and adds some flavor to how well you can combo. My combo deserves to be cut short if I miss a cancel, in the same way that I don't deserve to complete my ultimate Street Fighter combo if I miss a silly button input halfway through.
I will admit that cancelling is kinda broken in this game, since it removes all landing lag, and creates such a massive difference between those who can and can't do it, but I love the idea. Keeping a vigilant eye, watching out for yourself and putting that arm out to break your fall does add more depth to the game.
If we were to ignore cancelling altogether, what makes more sense? A game where you have landing lag when you fall while your legs are outstretched in a split, or a game where you hit the ground and stand up immediately, regardless of if you're landing on your head or back or something? Autocancelling is just plain stupid. If you're going to remove cancelling, you need to leave the landing lag (barwl) or you'll end up with a broken game where aerials are unpunishable, easy to execute, and zero risk (relatively speaking).
YES I KNOW THE LAST PARAGRAPH IS CONTRADICTED BY SMASH64. I'M SAYING IT RIGHT NOW: SUPER SMASH BROTHERS 64 IS BROKEN. PLAY MELEE INSTEAD.