Plus, what about all the third party web sites that offer nice buttons that say "Sign in with Google"?
If you used your legacy Gapps domain to authenticate, do you think they all provide easy implementations to migrate your Google-one-click-authentication account to a same-email-new-local-password account? Hell no.
If such a service only saved the email address when the user account was created it might be very difficult for them to fix this unless the do it really quickly and I happen to sign in to their service before all of this goes down.
It's honestly just a chore, many things don't work using G-Suite accounts, like taking part of a Google Home family with Gmail users, or signing in to Android Automotive (yes, I had to make a new account to be able to sign in to my Polestar 2 because my account is a G-Suite account), I would be HAPPY if they "downgraded" me to Gmail with custom domains and charged me a few bucks a month for it.
If Google introduced a "Legacy GSuite Mail' plan at say $20/yr to retain all existing mail functionality and accounts, and disabled every other Workspace feature, I'd gladly pay for that.
I dont really need any more service than I have now, I don't need the full google workspace, I just want gmail on my custom domain, thats all really.
The most annoying parts of this, google, the company that hosts my email, couldn't even be bothered to send me an email about this, I instead found out about it on the front page of HN.
So now I need to figure out how to migrate out, because if I move my email, I have to move my entire google account, my email, domain hosting/registration, youtube account, everything, I have no way to port the data over even to a regular account.