Revision is an integral part of the writing process. I won't say it's the majority of the effort, since in my experience finishing the first draft takes more work than anything else, but I'd estimate revision is still like 25%. If you want to be a good writer, you need to learn how to do it yourself.
I think it's okay to use external tools to find spelling errors and typos. Ideally you fix them yourself, so you train yourself not to make them in the first place. Grammar checking should also be fine, and again, ideally you fix your own words. These are all things with pretty clear right/wrong answers most of the time (although rules of grammar can be broken occasionally by good writers).
You could also have an LLM review your work and give feedback, basically having it play the role of an editor. This might be okay, but I'd advise extreme caution. How well do you understand the biases of the AI model? Studies have shown that people tend to put way too much trust in LLMs, and anecdotally talking to people I know who use AI for various things, I've been shocked at how much they trust it. In any case, in this mode of interaction with the LLM, you keep your own words at the end, but it still won't necessarily make you a better writer unless you can pretty deeply reflect on what it tells you.
However, anything else where the AI directly makes edits to your work is by definition changing your voice unless it's really small stuff. You are no longer writing in your own words at that point.