If you do decide to move away it may not be as bad as you expect for the everyday email, contacts, and calendar.
In particular when it comes to your email you probably don't need to manually use IMAP.
I've migrated thousands of emails between different providers a few times, the last one being GMail to O365 then on to Fastmail when I decided I preferred them. Each occasion only took quarter of an hour or so and didn't involve manual work or IMAP downloads.
The not-so-secret secret is that many providers include the ability to import directly from other providers. In the case of Fastmail (which I've now used for years and totally recommend) their import options include IMAP but also include direct connections into GSuite to do it for you - in the background that option also uses IMAP as it happens, but other than providing the connection details they do the transfer server-to-server without your involvement.
Then you can copy over contacts as Outlook CSV files (which are recognised by most services), and calendars by exporting then importing ical files (connecting calendars only works until the connection breaks, in this case by your G account being switched off).
