I had the same problem my first time with guildhests. I started them late, but I'm no stranger to MMO group roles. Still, people were treating these like FATE battles, just trying to kill everything in the shortest amount of time for the best bonus. Unfortunately, people trying to learn new roles simply will not have a chance to read the objectives in guildhests. You might be able to review the pop-ups from the in-game guide, though.

It's truly the one area that falls flat on its face: Teaching people how to play group roles, but not many people want to bother reading what it has to say, even if it's vital. What's more, is that I think there's an achievement for doing a certain number of guildhests, so you get some people wanting to speed run it like a dungeon.

By the way, I think the OP is my evil twin doppleganger....... >.>