Unfortunately, the laws of physics and the universe we live in make this very difficult. Due to the speed of light (and internet speeds) it can take a signal from your location to our servers up to 250ms to be received.
Every other MMO fixes this issue by having their servers much closer to the players so you don’t notice this. But we wanted our game to connect everyone worldwide which means that I can play here (in the UK) on a server on the west coast of the US (~150ms) with very few problems. We try to start players on worlds nearby to them but portals make it very easy to end up on a server on the other side of the world.
What this ultimately means is that when you shoot the server doesn’t even know about it until 250ms later. Which is why we need to cover it with a pause.
Another insanely complex solution would be for the server to rewind history back to when you shot the creature and kill it there (also undoing any effect it would have done to you) and then playing time back fast forward to the current time. This would result in a really cool effect that each time you kill a creature the timeline splits into 2 and the creature world die instantly for you but later on for everybody else with the corpse in different places for different players. Now imagine what would happen if 2 players shot that last hit at the same time…