It's less that it isn't balanced overall, as someone pointed out a few posts ago it's apparently 79 total animations and 19 are vore/unbirth/absorbtion, but what has people complaining is that almost all the vore scenes are for the female enemies, which a reasonable number of which don't have alternate non vore scenes.
People want to see other things from the female enemies, and have multiple times now, not gotten it.  Not all the time, there are female enemies without vore scenes, but people are more likely to remember the bad than the good, and it is disproportionately females using vore, so they get grumpy about it.
Honestly, they complain so much, because what we do have for non vore fans is fantastic, so everyone is invested enough to be very disappointed everytime a new female enemy gets released that has only vore.