If you were right, then autoclicking wouldn't be as popular as it is. Why is it more effective to click fast, if clicking 5 times per second would be good enough?
You are right in some ways, if you click 5 times per second or 10, you'll do the same damage to an entity, but a player isn't a zombie and works different, even though they are both entities.
Do a test, try clicking 5 times per second and look how much knockback someone gets, and then do make an macro so you can click 15 times per second. Me, and others have tested this before - you get more knockback and it's way easier to hit people while being in a combo. If autoclicking, or clicking fast at all didn't give an advantage it wouldn't be this popular.
Why are there people that doubleclick? Why is that even against the rules if it doesn't give you an advantage? You are clicking, so your aim won't be as good as if you were not clicking, clicking (over) 5 times per second is extremely easy and almost anyone can do it with no to little practice. But if you use a double click macro and click 10 times per second instead of 5 - you randomly start doing better in fights, while actually nothing has changed following your logic.
Why do you give more knockback if you click fast, why is it easier to hit people if you click fast, why do people complain so much if it's not an issue at all? Why is autoclicking against the rules if it barely gives an advantage, yes you might get better aim if you don't have to click, but with a little practice your aim barely even changes if you click (unless if you jitter, but jitterclicking is useless to then) You won't do more damage if you click 100 times per second or 5, but it gives more knockback, you will get the next hit even if you are the person getting combo'd, fast clicking can give a huge advantage over people that click only 5 times per second.
Autoclicking doesn't do much in a fight.
If I would be autoclicking, let's say 20 clicks per second, I would litterally combo you up in the air and you would not be able to do anything about it if you would be clicking 5 times per second.
But if we would both be clicking 5 times per second, the knockback you get will be similar and is based off ping instead, and knockback is extremely important in fights these days; the more knockback you give, you bigger the chances are you will win.
Because of ToggleSprint, you are able to combo and sprint and the same time without having to tab your W-key. Which means, if you give a lot of knockback you can still sprint towards them and keep hitting them until they jump and receive enough knockback to be out of your reach. They also can't hit you because on their screen they will be out of your reach because of the knockback; which is called a combo.
Minecraft does not register anything over 5 cps so all of the other clicks mean nothing.
I probably said it at least 5 times, but I'm gonna say it again - the clicks mean a lot, but you won't take extra damage. If you would, no one would play it anymore.
You indirectly do take extra damage, because as I said earlier, fast clicking and/or autoclicking gives you the advantage in a fight, if you get somebody in a combo (which will be easy if you click fast) you will be hitting them a lot more than they can hit you, which results them indirectly taking more damage, and losing the fight.
I probably repeated myself multiple times, but I'm trying to make clear that, yes, fast clicking DOES matter. And it's useful, not useless. I rushed this wall of text, so if you still disagree I can take my time to proof that I'm right in this one.
TL;DR In short, you're right. If you click 100 times per second or 5, you will do the same damage, but it helps you in fights a lot because it's easier to hit people first, makes up for missed hits and you give more knockback which results you in being "better" than others and winning more fights.
lol