Do you want to know why everyone is a sword user? Part of the issue is these darn bats. They hard counter gunners.
Greavers can infinitly gap close onto a knight, impossible to kite or knock away.
They get to attack multible times, impossible to block.
Their is not strategy to fighting Greavers, you just have to face tank them and kill them fast, which only sword users can do.
I can solo tier 3 arenas and CSKs, but as soon as one or two greavers spawn I just have to return to haven because I'm a gunner and they can't be dodged or kited and I don't have the damage to kill them with one hit like a swordsmen with a flourish.
It is completely possible for a gunner or even a bomber to counter greavers, and the way to do that is by learning how to time things. Greavers will always stop their attacks upon being hit by anything. A skilled bomber will know when to place bombs such that they will detonate right as a greaver starts its dive. A skilled gunner will shoot the greaver as soon as it starts its dive.
I primarily use bombs and guns. Only recently did I get a sword higher than 3*. The decision not to use a sword comes with its advantages and disadvantages - bombs get crowd control and AoE damage, guns get range, and these benefits are traded for the inability to quickly dish out damage to nearby enemies (unless you unload a whole clip point-blank). Unless I make a mistake, I never have any problems with greavers when I'm using a Shivermist, a DBB, a Silversix, or a Radiant Pulsar.
In my opinion, greavers do not need a nerf. I will admit that they are quite possibly the hardest mob in the game, but that's what makes them fun.