I'd draw it out as long as possible. I guarantee they'll do something shady to make the case dissappear once they realizing it's ruining some internal metric, and you'll get a laugh out of it.

I find almost all B2B SaaS solutions really bad to handle payments (even when they use Stripe).

Google does not care. They don't have to. They're a rich monopoly. Beyond that, they've always been bad at offering support and any kind of connection to users. It might be because they grew up serving free users of search and email. But that culture is how they run their services for businesses too.

Your other choice is to pay the other monopoly, Microsoft, who just recently revived their 90s strategy of bundling Internet Explorer with Windows, except with Teams and Office. They may have slightly better support than Google but it is built on products that get more expensive over time. Office does have offline clients that don't have these types of issues as often though.

I hope there is some kind of push towards alternatives from others but who could those even be? Proton? OnlyOffice? Libre Office? No one seems like a serious challenger in this space, because it would be so hard to compete against Office. There is little investment interest here and so there is little competition.