Well I had people last week that were awful if that's what you're asking. Legacy players though might be a special kind of awful. There's probably some good guilds in them that were doing all the hard content first and what not but most of them are you average shitty player. In fact considering how shitty the game was, if they played it up to 50 and for an extended period of time after that, it's safe to assume that they had mental health issues. Not surprising they're still dumb as shit now.
I guess it'd be nice if Legacy had to queue with their own servers, or at least we had the choice. There's a few threads about it already, all of which have legacy players crying about segregation, racism and whatever fucking stupid reason for it to be shared. To be honest I'm even surprised they kept legacy players at all. I would have wiped everything clean. Keep titles, mounts and other random shit like that, but wipe the chars, wipe the economy. Wouldn't be an issue then. It's even worse because at launch they won't really have to do low lvl content right, they'll just start at 50. Only that other than the ones who played the beta extensively, most of them won't have a clue about how their classes work. I'd be interested to see the first raids on legacy servers when the servers go up, should be quite hilarious to watch, maybe I'll catch a stream.
Anyway mostly not an issue really, at launch there will be people to group with, and you can join a guild and group with friends so you don't really have to use the LFG tool. Considering dungeons are pretty much the best xp it seems, I assume every guild will have dungeon groups going non stop and shit.
