No it’s not more secure going via Gmail. But what I did was to get the paid Proton Mail and I used my own domain name. So yes plenty pain and time now to slowly update my email address everywhere away from Gmail to my own domain name with Proton Mail.
But hopefully it’s the last time I have to update the email address everywhere, because even if I leave Proton Mail, my mail address is not tied to them, but to my own domain name so I can point that to any other mail provider.
So every mail address I’m changing now, is one away from Gmail. But if course 99.9% of businesses don’t Encrypt mail, so I’m only really cutting Google out of the loop (assuming the other party is not using Gmail of course).