The problem with hellbat drops is not that they are overpowered in any particular non-mirror match-up. In fact, they can be shut down pretty easily if scouted by the zerg or protoss opponet.
In TvT however, they can utterly dominate if not prepared for (or even so), and that is the problem. The Hellbat Drop strategy is becoming so efficient in TvT that it is becoming the goto strategy for many prolevel gamers and is supposedly creating a stale meta-game within that MU which is bad for the sport and viewership.
-Why it shouldn't be nerfed
The Terran race by design is built to do early damage. Terran has a variety of options to go for in order to harass the opponet and kill workers, hellbat drops being one of them. If you are unprepared for the drops, they can devistate the mineral line causing huge economic damage. But you cannot at the same time say that the strategy is overpowered whilst not being prepared for it. This is a lot like saying," my MMM ball got destroyed by 4 colosis. Colosis OP." when you have zero vikings. It's just all about scouting and preparation.
Nerfing the hellbat could have serious consequences in the early game for those who play mech in nonmirror match-ups. it could make the hellbat simply too weak to hold off early all ins and just break the mech play-style for good in HOTS(since it is already pretty weak). So not only will the mech playstyle be endangered, but you will also eliminate another strategy for terran in order to do economic damage.
-How to fix it with a buff, not a nerf
When going for Hellbat Drops there is a huge weakness, no AA. What blizzard needs to do is buff the banshee. Buffing the banshee would take care of the hellbat strategy in TvT while still leaving the HBD viable and not making mech even weaker early-game.Blizzard says the want more exciting games, and seeing HBD every single game certainly is not that fun to watch, but it is a strategy that should still be viable within the Terran arsenal. Just buff the banshee and then let the meta evolve from there. Now that the other races have earlier detection this should be a problem if scouted.
And the banshee could use some loving anyways <3