I've always felt Valve's numbers are misleading. I would like more hard stats from them. I don't think Valve is as nearly as popular as the big 3 in North America. Instead I think Steam gets a lot of users in places like Russia where consoles are not readily available.
Also, I personally don't use Steam. If I do get a PC game it has always been from gog.com. Given the rise of the Epic Games store, I might consider them as well. So you can count me as the type of person who might use the Epic Games store but not Steam.
You should actually take advantage of all the stores on PC. No need to do a "boycott" simply cause you dont like a certain company. There's bundles, free giveaways, and sales that feature on pretty much every store (minus Bethesda).