What you did was not vandalism, but it was rude, since it violated the moral right of the other user to control the words associated with their authorship. When one contributes to the article space, one is explicitly relinquishing that right, because Wikipedia is a collective effort, but that does not hold for talk space content, particularly when it is signed.

And what you did was doubly rude because you acknowledge that your version was "preferable"; that is, it is conceivable that the other user prefers their version. They may be wrong to do so, but by editing their words directly you are denying them their right to an opinion. It is not surprising at all that your edit was reverted.

Yes, I agree, in hindsight, that I was rude according to what I discovered (the hard way) be the prevailing norm.

However I have difficulty agreeing with you on your second paragraph, indeed it is the exact opposite of what I deeply believe: I am convinced that there is an objective truth, and that one of the things where there is prevailing conviction as to what is correct spelling wand what is not. Words have meaning by virtue of convention, and if you do not pursue the convention, you are reneging on the certainty of being able to unambiguously and intelligibly commune with others.

Words change over time. One of the big reasons is being prone to misspelling.