Well, it isn't as simple as that. I play a tamer mage and I die more easily to mystics than I do to just about any other template. I have had problems with ninjas but when I remember not to try and run away from a death strike they aren't so bad. Mystics are currently doing the highest dps on average against me.
And as I already mentioned, I'm getting hit by the effects of mysticism spells when I am well off screen from any enemies. I know one of the culprits is hail storm, and I think the other is spell plague. And the sleep spells are also very powerful.
The thing about archers is if you have a combat skill they aren't going to hit 100% of the time, unless you have a run of bad luck. The same goes for dexxers unless they can disarm you, and even then they aren't as deadly because you can generally run around until you can rearm.
With mysticism there is no defence other than to start running as soon as you see one.
But it's hard for me to say categorically that mystics are op, because it is generally a pretty even fight with me when it is a one on one fight, and for me to start whining about being beaten up in a gank by skilled pvp'rs is a bit ridiculous. The only thing I can categorically state right now is that I die to mystics more than I do to any other template.
The other indication that maybe mysticism needs some balancing is how many are using it now. Basically it is to the place where almost all of the really effective mages are using mysticism, and they are the current kings of pvp in UO. But then again, maybe it isn't that anything needs balancing, maybe I just need to adapt.
I'm not a big fan of the nerf bat at the best of times, so if there is something I can change in the way I play the game, without jumping on the bandwagon for the latest fotm, then that is the way I would rather approach it, and not start screaming and yelling for the devs to play my game for me.
So as I said, I'm waffling...