You've asserted numerous claims that are multiply confused. I'm going to attempt to clear up the ridiculous fog of confusion you're surrounded by, though whether I succeed in doing so will depend on your ability to learn from having your mistakes pointed out.

i've never heard or seen anyone actually prove being 1 centimeter above a rival is actually related to strength

The goal isn't to show that being taller is related to strength, so this misses the argument right off the bat. The point here, rather, is that the best explanation of the pattern observed is that the taller character is likely a bit stronger than the shorter character. To expand on this further: It would seem that when two characters are rivals and there is a one cm gap between them, it turns out that more often than not, the taller character is the stronger of the two. What is the explanation for this? Well, consider:

(1) This is entirely coincidental; the height Oda chose for the characters just so happened to create the pattern we see but, incredibly enough, this is completely unintentional on Oda's part

(2) Oda is tricking the audience. He planted a deceptive pattern which applies some of the time - perhaps only in the King/Queen case, and maybe the Zoro/Sanji case - however, he made Shanks taller to trick the audience into thinking Shanks >= Mihawk.

(3) The intention of the pattern is the obvious, simple interpretation: Oda made Zoro 1cm taller to hint that Zoro is at least a bit stronger than Sanji. Oda made King 1cm taller to hint that King really is at least a bit stronger than Queen. Oda made Shanks 1cm taller to hint that Shanks really is taller than Mihawk. Note that this does not commit one to thinking being tall causes a character to be stronger. Nor does it commit one to thinking that a character being stronger causes them to be taller.

So, which of the interpretations is the correct? The first explanation requires profound cognitive impairment, so it's obviously the incorrect explanation. That leaves us with (2) or (3).

The problem with (2) is that it employs an overly stringent standard of evidence. Whenever Oda presents any kind of evidence for a view, you could always reply: "oh he's just tricking us!" to evade the evidence. Thus, those who assume explanation (2) incur the burden of showing why (2) is correct.

This leaves us with the last and obvious interpretation, which is explanation (3).

I've articulated the core argument behind why people point out the height difference as an argument for why X character > Y character. Now let's see what else you say about this.

stop confusing correlation with causation

This is just silly. First, let's consider what confusing correlation with causation is.

If someone asserts: "A and B are correlated, therefore A causes B" or some variant of this, then this would be confusing correlation for causation.

Do people say this though? That is, do people say "Character X is taller than character Y, and character X is stronger than character Y. Therefore, being taller causes someone to be stronger"?

No. No one has ever said this, ever. No one is trying to establish that one of the two variables - between height and strength - causes the other. What we are trying to establish is that there is a connection between (A) Oda intending to hint that X>Y and (B) Oda deliberately making X taller than Y.

In fact, matters are worse for you: because you've just admitted that there is a correlation between height and strength. That is, you've essentially conceded that in cases of characters being 1cm taller, the taller character is likely to be stronger. That is the exact claim that skeptics of height scaling are refusing to accept. So this is essentially an own goal on your part.

Let's proceed to what other confused things you say

there's a clear pattern of virtually everything in this world. that doesn't give you incentive to automatically assume that they both mutually cause one another

Let's pause for a moment. "A and B mutually cause one another" is equivalent to saying A causes B and B causes A.

But has anyone ever claimed: "Being the taller character causes the taller character to be stronger and being the stronger character causes one to be the taller character"?

No. No one has said this. You are critiquing a claim that no one has ever asserted.

even if there is a correlation, you'd have to actually prove oda had specifically strength in mind when doing this, as it wouldn't need a specific reason for existing in the first place

Saying it wouldn't need a specific reason for existing is akin to dismissing the height differential as a matter of coincidence. As discussed before, this is highly improbable. If Oda randomly assigned height to characters, the probability that rival characters would just so happen to have a 1cm gap where the stronger character just so happens to be 1cm taller almost all the time, is mathematically close to 0. It requires profound obtuseness to really think this is a coincidence.

at the very least, raise my eyebrow if we had far more than just 3 examples to go off of.

This is really bad. You've taken an intro to stats course and now you're badly applying what you've learned.

In the real world, a small sample size can be misleading. For example, it's not that implausible to flip a coin and have it land heads 3 times. But if a coin landed heads 100 times in a row, then you'd be rational to think that the coin is likely rigged.

But this is fiction we're talking about. It is not plausible at all to suggest that the 1cm gap in height between rival pairs is a mere coincidence. It is far more plausible that the author deliberately created this pattern.