Okay, I finally got the Owlbears and checked them out in a few things.
I have to agree with everyone who says that the PRR doesn't seem to be working. I've ran some quests and wilderness areas with all both Owlbears and the Onyx Panther at the same time. The two Owlbears seem to be taking about the same amount of damage and the Onyx Panther is definitely outlasting both Owlbears. Evasion might explain the Panther outlasting the Owlbears, but I would expect the Epic Owlbear to be receiving less damage than the Heroic Owlbear.
As for damage, the Owlbears seem to be doing fairly nice damage, but they are slow. This is fine when they go one-on-one with mobs or the Owlbears are working in a group, such as two Owlbears and the Onyx Panther. However, if there are multiple mobs with a single Owlbear running, the slow but steady output from the Owlbear is too slow while the damage the Owlbear takes is too much when in level appropriate quests/areas.
Cleave and Great Cleave are definitely broken on both Owlbears. The only time I've seen those abilities go into cooldown mode is when I am spamming the button for them. I've not seen either hirling actually use it on their own. Not only do these feats appear to be manually active only, they don't seem to work about 80% of the time on the Epic Owlbear. Since there's no special animation for the cleaves, the easiest way to tell if the cleaves work is to go to Kobold Assault and test it on the mobs there. The Heroic Owlbear cleaved whenever I spammed it, but the Epic Owlbear rarely cleaved when I spammed the buttons. Now for the completely sad part about Cleave, Heroic Owlbear only does 10 damage, which the Epic Owlbear did 16 damage, with one crit for 32 damage and 46 slashing damage. Very, very sad.
I'm going to still stand by my expectation that these Owlbears should have a Sweeping Strike type attack. Heck, the only Owlbear mob that we've encountered so far does a decent job of knocking players down...and knocking the Heroic Owlbear hireling down.
After testing out the Owlbears, I'm a bit disappointed by them. IMO, the Panther is superior to both Owlbears. I'm hoping that the Owlbears do get fixed/finished. The Owlbears are diamonds in the rough, I just hope they aren't another Turbine project that is left unfix or semi-working.