It's probably computational intractable for the server to do a significant part of the work, especially given it has to work harder than the client as the server operates with inaccurate information so it has to think harder to compensate for this shortcoming. This is why virtually every MMORPG has client doing most of the work. There's nothing inherently wrong or cheap about requesting an update from your client every 0.3s. I remember way back in vanilla WoW, there was the positive/negative polarity effects in Naxxmas the server used to check the status frequently and it simply overloaded the server, so they had to reduce the frequency the polarity buffs are checked because otherwise the server can't even handle all the information on time. Keep in mind despite MMORPG's seeming complexity, at its core the server is just rolling a bunch of RNGs against a formula plus some scripts, so the servers aren't exactly this mega powerful machine everyone assumes it is.