The issue with the Ubisoft case was that Ubisoft offered R6S in a free, restricted mode and a full mode. However, Ubisoft allowed you to obtain the free version from Steam (distributed by Steam servers) but offered a cheaper way to access the full game on Uplay only.
So you could get the full game, distributed by Steam without spending a penny on Steam, as long as you purchase it on Uplay. That's just Ubisoft trying to dodge Steam's policy prohibiting cheaper access to Steam distributed games on other storefronts.
It's kinda like you providing a free game on Steam, but upon opening it you have to enter your credit card details first in order to access the rest of the game. You're just using Steam's services for free at that point, and that is obviously dodging the policy.