The best way to break that is to not sell games on Steam. Another way is what Epic is also doing, giving away free games to build up people's library on their store as well.
Not really, I personally go and buy it on GOG. Sure, Steam is the biggest store these days, but there is competition. And it's good when developers release in all stores. That's the proper way.
Exclusivity is a bad method to fix monopoly, since it simply creates another monopoly. I.e. if you had one problem, now you have two.
Maybe you're thinking of the Humble Bundle? Many products there are sold as Steam keys.
But if there was a single interface and all I had to do was add my credentials for store X? That's not so bad.
For every person that buys directly from the developer, I expect there are several order of magnitudes more people that buy through steam. If you're a drop in the ocean, that doesn't count as "not really".
To state otherwise, it should have been written as "So when people go to buy one more game... the majority goes to Steam".
Also, the argument that a statement implies 100%, but it's actually a slightly smaller percentage is very weak, especially in online forums where people don't write legalese.