I think the point is that you don't abandon gmail right now, you give yourself an alternative, and when you access a service or decide to change something about it or need to recover an email, you change it then (and store the new info in your password manager, maybe mark/rename the old info as OBSOLETE if you have that sort of control), and eventually you've decoupled yourself mostly.
Truly decoupling yourself is hard, and you'll probably be finding old accounts and dealing with them for years, but getting 95% of the stuff moved over the next year or so will likely give you a lot of peace of mind if you're actaully worried about it.
FWIW if you're actually worried about it, you should also make sure your email is through a domain you control (even if just pointed towards a service, or even gmail) and that domain service is not linked administratively to the same account that you use for email (e.g. don't register domain through google and then point at gmail), so worst case you can change the destination service by changing MX records and just swap all your email at once to a new handler (or if you're a masochist or as a last resort point towards your own mail server you admin). Just make sure it never expires (in the end, there's always something to worry about, you need to find the risk you're most comfortable with).
Truly decoupling yourself is hard, and you'll probably be finding old accounts and dealing with them for years, but getting 95% of the stuff moved over the next year or so will likely give you a lot of peace of mind if you're actaully worried about it.
FWIW if you're actually worried about it, you should also make sure your email is through a domain you control (even if just pointed towards a service, or even gmail) and that domain service is not linked administratively to the same account that you use for email (e.g. don't register domain through google and then point at gmail), so worst case you can change the destination service by changing MX records and just swap all your email at once to a new handler (or if you're a masochist or as a last resort point towards your own mail server you admin). Just make sure it never expires (in the end, there's always something to worry about, you need to find the risk you're most comfortable with).