i don't know if there is a way to kill all the spawner mobs at once and every time i asked in chat the answer was no, clicking around 2000 times is really straining so i wanted to ask here: is there a way to kill all of them or did you people find a way to make it quicker
if your only aim in killing the stacked mobs is to get rid of them without considering the experience and items to be gained from killing them manually, then feel free to put some lava buckets on them for the mobs to be killed instantly.
But if you're aiming to get the experience and items from that specific mob while killing them all at once, then that would not be possible. That's why it's called GRINDING, it should not be naturally easy to do.
I suggest you make a grinding sword with some custom enchants to make your grinding much more efficient. And to help out, here is the current list of enchants I put in my grinding sword.