Eh, the damage die isn't the issue, it's modifiers. Yes, they can do the Power Attack thing like a Fighter can, but a Barbarian still does it better. Hell, a Rogue can probably out damage them much of the time.
As for the Animal Companion: if you have to rely on another creature to fight your battles for you, one that isn't even a unique class feature, that's not a great thing.
Pounce: Psy Wars get Psionic Lion's Charge at level 4. Barbarians still get it at level 1.
Also, if you take Pounce at level 4, you can't get Natural Weapon upgrades until level 5, which slows your damage further.
Them being scouts/skirmishers is great, it really is, and they seem very very competent at it (the scaling mechanic in the skill beast powers is a nice touch), but they still need to DO something in combat. Right now, they don't have enough. Scouts get Skirmish even! Scouts, the class that the Beast Master is DIRECTLY competing with for party role, get extra damage on their attacks. The Beast Master can't compete with that currently.
At the worst, give them some more beast powers that let them tap into the ferocity of the wild, gives them more damaging abilities. That way, you can be a scouter and still be able to kill dudes on your own, just in case. Options never hurt, right?