Why not just download your old mail and archive it then? Google provides an easy way to do this (Google Takeout).

As in, I don't see the problem with having more storage - you use only as much as you want.

Personally, I find having all my mail searchable from any computer useful. And Google does provide lots of security features (2FA, suspicious login detection, new login alerts, login audit logs etc)

I typically export mail regularly. In my case, I store them in a DEVONthink Pro Office database as that supports directly importing from Apple's Mail.app, has good search, and good cross-referencing support.

I really wish I followed this practice sooner as there's mail from the 90s I wish I still had. I've used e-mail continuously since 1991 so it would be a lot of mail. Disk space is the main reason why I didn't do it sooner.