In many experimental sciences, a lot of research projects now require an effort that a few authors cannot handle. There are some discussions if this means that

In many experimental sciences, a lot of research projects now require an effort that a few authors cannot handle. There are some discussions if this means that instead of being creative, people are merely scaling up, which is probably true in some cases, but often strong empirical results that enable "real-world" progress require such efforts. But that's not Math. I work (partly) in a field of theoretical CS which is Math-heavy and attracts mathematicians and there I also feel the indirect effects of Covid-19. As a junior in the field, I need to rely on the feedback of more senior people, and these people move fastest on the whiteboard/with pen and paper, in physical meetings. The good thing about these collaborations is that we juniors can provide fresh ideas and the seniors can shoot down the bad ones quickly (before a long, formal review process) and make sure the good ones are executed with the necessary rigor. (Note: I find the comment of "your" reviewer strange as well.)