Is it impractical to never send a message through Google? Probably, depending on the circles you communicate in. But that's not the same thing as saying it's impractical to avoid Google for most of your messages, and certainly not the same as saying you can't avoid GMail for anything.
Like I recently had to turn off alias for made4men.no. srsly, signing me up for spam and not removing me from the spam list even after i unsubscribed. You can tell it's a swedish shop that just happens to own a Norwegian domain.
I actually had to do the opposite. I have a filter that catches all messages marked as spam and unmarks them as spam. VERY rarely there's a spam message caught in there. Much more often sth super important that just would have landed in spam if not for my genius spam filter.
But it's plain false. YOU can decide against using gmail. I don't use gmail. I sometimes talk with people who use gmail, but more often than not, I don't. Stop being fatalistic.
They are saying you are using Gmail when you communicate with someone on Gmail.