The Cometeor timing happens in JP groups irrespective of voice communications; the leader simply throws down a marker or two when everyone signals that they're ready in text and does a countdown so people have a chance to use their crowd control. Bam, half a dozen perfectly-timed AR explosions and most of an entire team wiped out. I don't know how it is on non-JP datacentres but blocking premades won't stop that in the slightest; most steamrolling GCs are just 1 sensible person with lots of macros and a bunch of randoms who follow orders. Personally, I don't mind it the way it is (Slaughter is ridiculous but it never pops any more due to the level cap).