Tbh, explosive bullets is really hard to balance because the idea itself is already OP, also mike said those vehicle will be used for most wanteds only you can check mike's reply
here. If you're really annoyed with the hydra it's quite easy to counter them just go around tall buildings they won't be able to hit you without changing to VTOL mode and if that happens just run away from the area, rinse and repeat. For the hunter, just pick a fast car you can outrun it or go around tall buildings same like hydra that works too or you can do the classic way go inside a tunnel and wait for them to come down and engage you on-foot. If you want to counter a tryhard, be a tryhard.