Wow, that title is a little hyperbolic, don't you think?
All said though, there is a kernel of truth to OP's opinion.
Glaive cav really isn't much of an issue in Skirmish because of A) archers and B) the fact that most cav use spears/lances -so it's not really viable in a match, but I can see how glaive cav might make the other game modes (Siege, Captain, TDM) much less enjoyable thanks to how (objectively) broken its mechanics are.
The same thing has been said about menav cav for almost 12 months now.