This is a self-fulfilling prophecy. If everyone reads "it's impossible to avoid gmail, just use gmail", then yeah, gmail prevails.

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.

I think they are being more factual than fatalistic. You just differ by definition of “use Gmail”.

They are saying you are using Gmail when you communicate with someone on Gmail.