So this might seem like a simple fix, "don't play on high ping servers" but that's not an option. I'm based in Australia, my friends are based in the US.
While I've definitely tried to suck it up and deal with the desync between server and client, combat is awful. In a single player game, I can fight and deal with enemies quite well (except when I pick a fight with too many enemies haha)
But in co-op with my friends in the US, it's impossible to have any enjoyable experience with co-op due to the reliance on server authority for combat.
In a PvP game this makes a whole lot of sense. But with PvE combat, server authority means that enemy AI behaviour will always win out over the difference with a player dealing with 250-350+ ping
My suggestion/complaint is around the dependance on server authority to handle combat, especially with a game where attack / parry timing is so important. I block and have enemies attack through a block without affecting posture or attack an enemy only to deal no damage because of the AI behaviour being tied wholly to the server.
In the case of a PvE game like this, is it reasonable to ask for more client-sided combat behaviour to mitigate issues like this, as I understand high ping will always cause issues for players in some way.