High ping means there is a bigger delay in communication between you and the server (200 to 400 is a very big jump, that shouldn't be this much - Finland is closer, so that's a bit weird). For most players it should jump by 20-40ms and that's generally not very noticeable.
The lag we were having was what turned combat into the equivalent of some dragon ball Z fight where everyone teleports and rubber bands on your screen, and the only thing missing was the sound effect to make it a full anime rip off. Ideally, and it seems that it's the case, the server switch has made Vegeta stop playing on the server.
To answer directly, it's delay vs stability. You can play with slight delay, but low stability means weird stuff happens and it starts becoming unplayable.