Let's take a step back and ask why we ask questions on a StackExchange site. The underlying reason is that we're seeking answers for a question we may have. To be intellectually honest, we need to accept that we may not like, accept, or understand the answers that we're given. And we also have to accept that we don't already have the answer. If we already know the answer we want, why are we asking the question?
While it's okay to disagree with answers, it's not okay rewrite the question via edits that end up invalidating existing answers. Invalidating answers is rude. Community members took the time to answer your question as it was phrased. It's impolite to get into a war of words because of either a misunderstanding upon your part about the core question (e.g. you changed your question) or a disagreement of what an answer is trying to provide.
The following comment from you indicates that you understood that your edit invalidated the original question.
This is a nice answer, but please see the update. – nalzok 11 hours ago
And let's also address that there is zero need to be antagonistic. In the rolled back edit, you ended with:
By the way, Stack Exchange has a Data Explorer which allows you to execute SQL statements. Does it make you feel insecure?
Given the tone of the comments and the rolled back edit, this comes across as antagonistic and unnecessary.
Let's address some of your questions here in meta:
Is it appropriate to rollback his edit?
It should be clear that the answer is "No." Your edit invalidated answers, and the rollback undid the invalidation.
If it's not, how should I rephrase?
I don't think that you should within the question that you asked. You asked "Why not use SQL instead of GraphQL?" and your edits diverged into focusing on the security aspect. You may have a separate question based upon the edits, but those rolled back edits should not go into the original question.
For another tack on all of this, take the perspective of a first time viewer to your question. Maybe they googled "SQL vs GraphQL" and landed at your question. The very first thing they would have seen is:
Response to commenters/answerers
and then a mini-diatribe on why the existing answers are wrong and there are serious security issues. To unwind things and understand what's going on, they have to read through a lengthy post that jumps perspectives as well as reading through 20 comments to get a solid gist of what's going on.
If they're feeling particularly inquisitive, they may actually get to reading the answers that were provided. Keep in mind, they came to an SE site because of the networks reputation for "questions are asked, high quality answers are voted to the top." Wading through lengthy comments, word wars, and non-answers is forumesque behavior that SE visitors and explicitly trying to avoid.
The average first time visitor would have simply closed the tab based upon the rolled back version of your question. That's obviously not a good thing for the health of this site.
Alright, so what should you do in this case? You asked the beginning part of a question, and now you have additional concerns within the question. The answer is fairly simple - ask a new question. Provide a link back to the original question you asked. Then lay out your new concerns about the question and delve into the security angle.
For bonus points, mark an answer on your original question to indicate to future visitors that "this answered the question that I had at the time I asked the question."