I've heard this from a several posts this week. Genuine question: since maintaining GSuite is expect to cost $6/user/month and Fastmail costs $5/user/month, do you really find the $1/user/month in savings worth the trouble of moving email providers and losing Drive/Docs etc.?
I'm planning a move too, but Fastmail's price doesn't strike me as competitive enough compared to Google's price. Amazon WorkMail is $4/user/month and Rackspace Email is $3/user/month.