The things you call "nitpicky grammar errors" are often (in my experience) symptoms of a deeper problem:
that the student has stopped caring about raising the thesis to a suitably high standard, and has not grasped what "completed" means in the context. An unfinished thesis simply can't be marked.
First, get your own proof-reader, and get help in getting all of these problems fixed - your supervisor is too busy to be a proof-reader, and it's an inefficient use of limited supervisory time.
Why is the grammar sloppy?
For different students, the underlying cause will differ; some won't be writing in their native language; some are careless; some have weak language skills; some haven't grasped the importance of good grammar and spelling to clear communication and to academic publishing. I've no idea which of these is true in your case, or if it's something else - that's between you and your supervisor.
Whose problem is it anyway?
You don't care about your grammar errors. That is your problem, not your supervisor's. You are angry. Again, that's your problem. Trying to make it your supervisor's problem, will make an enemy of someone who you need on your side. You think your supervisor's comments on content are trivial, and that is also your problem, not your supervisor's problem.
And now this post has maybe made you angry too. And that would also be your problem, not my problem.
I say all this, because accepting that they are your problems, is the first step to fixing them.
Collaboration not conflict
The problem that I am trying to help you fix, is that your supervisor is telling you what you need to finish, and you seem to resent doing it. Supervision has to be a collaborative partnership, not a battle. Now, in theory, it's your supervisor's job to make it such. However, in some cases, in academia as well as in the real world, you often need to manage your manager - and that can mean you taking responsibility for ensuring that it is is a collaborative relationship.
So, find out what incentivises your supervisor, and try to put those incentives in place. Is it publishing papers? Esteem within the department? Conference papers? Get your supervisor on your side.
The worst case
And (take a deep breath): sometimes, when a thesis is genuinely bad, it's not apparent at first. All one sees on the first couple of readings, are a few errors here, and a few errors there; but when they're corrected, new problems appear.
It gets to be like "Star Wars the Phantom Menace" - the East Coast of the US produced one homebrew re-edit of it, to fix some problems; the West Coast produced a different homebrew re-edit, to fix other problems; but in the end, both re-edits and the original are pretty awful films: fixing the most obvious problems just exposed other problems.
I really really hope that's not the case in your case; but as this answer will hopefully be read by many people in your shoes, then at some point, it will be true for one of them. And at that point, that person and their supervisor need to think about a radical rewrite, or walking away from it as a lost cause.
Where to go from here
But for almost all cases, it's just a matter of getting your supervisor onside, getting a definitive list of the problems, and then you doing what your supervisor says is required to fix them. With them, write a checklist, and then return the checklist to them, with a note next to each one, stating how and where you've fixed it, or how you're defending it.
And finally - this post will inevitably contain spelling and grammar errors - it's Muphry's law in action. But that doesn't invalidate the advice in any way. With language, context is everything. This post is not academic scholarship; your thesis is.