I doubt anyone will complain if Blizzard's games are brought to other storefronts too.

I like Steam. Steam has the best features, best UI, good sales, and while they are not without faults (systems can stay unchanged for a long time!), they are run by a company that by and large respects its userbase.

I don't mind if games are brought to Steam and any or all other storefronts. Put it on GOG, Windows Store, EGS, Itch.io, battlenet, Origin, Uplay... You name it, I approve of it going there also. If those other storefronts want me to use them, they need to provide a comparable or superior experience. GOG comes the closest, but its inability to get games in a timely or predictable manner, if at all, is too much of an obstacle for me.