The barbarian's capabilities within the grapple will differ radically depending upon what the barbarian is using for weapons.
Taking a standard, by the book 18 strength half-orc barbarian 4 who wears a chain shirt and wields a greatsword, his damage goes down from 2d6+7 (+10 while raging) with the greatsword attack at +10 (+12 while raging) against AC 15 to 1d3+4 (+6 while raging) subdual which will only happen if he beats the bear's +16 grapple check with his +8 grapple check. Or, he can provoke an AoO by attacking with an unarmed strike at +4 (+6 while raging) against AC 15 for the same amount of subdual.
That's far more than a 66% decrease in the barbarian's offensive potential.
Taking a barbarian who thought a bit more about the possibility of being grappled, let's say that the 18 strength half-orc barbarian is wearing a silver spiked gauntlet, a locking cold iron spiked gauntlet, and masterwork cold iron armor spikes on his chain shirt. So he goes from 10.4 points of average damage per round (16.8 if he's raging and power attacking for two points) to 1d6+4 (+6 if raging) at +5 (+7 raging) to hit or 4.5 points of damage per round (5.7 if raging). That's a 40-60% reduction in the barbarian's offense right there.
However, when the bear pins the barbarian next round (quite likely to happen considering the bear's +16 grapple check against the barbarian's +8 or +10), the barbarian is finished dealing damage until he can get out of the grapple. That's a 100% reduction in offensive capability. The bear, however, will continue to deal claw damage with each successful grapple check to maintain the pin.
And if you change the barbarian to a fighter or speculate that he's used up his rage for the day he's even less likely to win the grapple and escape from the pin.
Grappling is the bear's schtick and it's pretty darn good at it. A dedicated PC ex monk barbarian grappler with improved grapple or a fighter/barbarian with combat reflexes and close quarters fighting might be able to give it a run for its money but, in a one on one situation or a situation where the bear's allies outnumber the PCs (what grappling is good for in general), it's very effective doing it.
FrankTrollman said:
The bear loses 2/3 of his offensive potential by grappling. The barbarian loses an average of 5 points of damage from the loss from the weapon, and only gets to use his strength bonus once instead of one and a half times.
Is that 2/3 of the Barbarian's offensive potential? If it isn't (and I don't believe it is), the bear is losing proportionately more by grappling than the barbarian is.
Which is the basic problem with this scenario: bears lose more by grappling than almost anything else can. Grappling is supposed to be their schtick - something is obviously wrong.
-Frank