Here's the thing about stealthies and melee in general, the best ones aren't using keyboard turning at all and have all their moves or at least their best moves keybound. They're very good at getting behind you and running through you and basically never stop running.
If a stealthy is doing this and running circles aren't you and you aren't able to do the exact same thing, they're going to be a very difficult opponent. Keyboard movement is slow, super slow, and they are fast. really fast.
It pains me to say it, since they are incredibly difficult to beat on my sorc dps because I'm not that great with keybinds and I use the mouse to click most of my moves.
Another reason they can be so difficult is the fact that they can wait out til their cooldowns are done before engaging, all the while being right beside you
All in all, I think their burst is a bit too high and I don't think any class should be able to drop combat into stealth indefinitely. Drop their burst a bit, raise their sustained dps and get rid of their combat drop. Sneaking is cool and it's their thing but no more dropping combat to heal when someone is out playing you when you probably already got the drop on them.