About GW's allergical reaction to Morathi: I think they were in such panic to nerf Morathi that they didn't really think it through.
Slaanesh cannot summon 1500 points a turn unless you've done something very silly. They are certainly (extremely) powerful, but you can play around their summoning. It has to be within range of a hero, it has to be on their turn, etc. I think its more of just the lack of interactivity Kroaks MW spam had. There was really nothing an opponent could do unless they had an equally powerful wizard to dispell.
The tools you have to play around Slaanesh's summoning are essentially the same you have to play around Kroak, namely murder all sources in a single turn based on what others are saying in this thread. More in general though, Kroak, as well as the other various wizard mechanics that've been nerfed, weren't any less interactive than certain other mechanics that are allowed to remain. At least spellcasting has unbinds, it's one of the very few mechanics where an opponent can directly interfere in your turn. And what I find funniest about all that is that the most broken wizard of all, who will keep on breaking every single interesting mechanic they can pull of with magic by sheer virtue of being such an outlier, hasn't recieved a single change to his immense casting powers. In general they just seem to be inconsistent with magic and not really know where to go with it.