Sorry SE, but endgame won't work if you don't fix something.

[Astarica]

this seems computationaly unfeasable to me but i could be wrong, however if you reversed it, server sends timestamp of when things are going to happen on the server this could work. couple that with the client sending a pos update immediately upon leaving a danger area and you would have a pretty responsive experience, internal server lag and race conditions not withstanding, its not really that hard to fix

Usually the reason to not have the client doing it is fear of hacking. It is much easier to hack your client than the server. As I pointed out your client lacks the ability to interrupt a spell the moment it detects movement, even though casting while moving is an impossibility. If it lacks authority to do that, you can be sure it won't have the authority to decide if you got hit or even where you are.