Sorry, who "seems to think this?". I haven't seen this claim, or anything like it, anywhere.
The point many were making was that the overwhelmingly successful suppression of all these other diseases was clear proof that "masks work" to suppress disease, and by extension that we should wear them to effect the suppression of a much more dangerous pandemic. So when there's a largely uncontrolled pandemic happening, you should wear a mask.
Now, general immunity seems to have reached a point where the pandemic is at least reasonably controlled without mitigation strategies. Covid of mid-2022 is now a worrisome endemic disease, comparable to (but yet rather more dangerous than) the worst flu seasons we've seen in the past century (since 1918).
So... we can take our masks off now (most of us, admitting that some people have different levels of risk tolerance, etc...). The calculus changes because the facts on the ground have changed.
None of that is an argument that you shouldn't have worn a mask in late 2020. You absolutely should have, and it remains horrifying to me that so many of us didn't.