Blood Knights changed the second BC ended, and considering they were only introduced when BC began, it's hard to pretend this is some new change.
You're about 13 years too late with your complaint. I find it hard to say that they ruined them when they existed far, far longer as their current incarnation than as their "edgy," as one person put it, version. Even though the "edgy" version acted exactly the same in almost every respect.
Otherwise it seems like people just applying what they thought was a Blood Knight onto what they actually were. They really haven't changed at all except for instead of using an enslaved Naaru they went back to the Sunwell.
Liadrin especially, much bemoaned in this thread, hasn't changed whatsoever in terms of attitude or story. And seems little more than a thinly-veiled thread to whine about Humans again, which took a total of one comment before getting there.