Some universities recommend avoiding gmail accounts for application process precisely for this reason (I can't find the reference). My personal experience is that open source spam filters (spamassasin/rspamd) are far better at classifying spam than gmail's filter.

However, there is another reason why no one should use gmail for anything serious. There is always a risk that you may get shut out of your account without recourse, taking down access to other services along with it.

This actually happened to me when I was an intern (many years ago). My official job offer went to spam and I didn't see it until weeks later. Fortunately I happened to check the spam folder and saw it. I now make it a habit to regularly check the spam folder in Gmail and I often find non-junk mail in there.