This is true if you're starting from nothing. However, Gmail is over a decade old at this point and is the primary email for millions of users. And something like custom domain is beyond the technical skills of average users.
However, Gmail is over a decade old at this point and is the primary email for millions of users.
Switching is annoying, but not impossible. You just forward the old address to the new and progressively replace it on any accounts you might have. I still have access to my Gmail account, it just hasn't received a non-spam email in years.
Oddly enough, it was really easy to set up a custom domain on Gmail: I did it. However, Google stopped offering that service for free, which will stop most ordinary people from using it...