There are several countries with very high vaccination rates. None are anywhere near rid of COVID. This isn't an argument against vaccination. I got vaccinated myself, and I try to convince other right wingers to do so (especially ones over 45). However, it's false to state that their failure to vaccinate has caused COVID to remain.
Regarding your "what is more harmful" argument, that can apply to anything.
If we reduced speed limits to 30 mph, there would be a lot fewer auto deaths. If we outlawed backyard pools, there would be a lot fewer drowning deaths. If we disallowed legal sales of alcohol, we would have fewer drunk driving deaths.
Rather than asking what harm it causes, why not ask if it's necessary to mandate? Masks suck and almost nobody likes them. We shouldn't be mandated to wear them unless we are getting a real, tangible benefit from them. I am seeing zero tangible benefit to children wearing masks in school, yet a lot of potential harm from it.