Almost all arbs are worth their salaries or they would have been non tendered before the arb.
The whole system seems flawed in some ways as things like what arb year is the player in seems to matter more than the performance level of the player in the previous season or two.
I agree that JBJ is worth $10M on the open market, but the arb process is far from "open".
The reason Mookie's arb number seems low compared to JBJ's is that Mookie's is a year one arb (out of 3). JBJ's is year 2 (out of 4). Kelly's was his final arb year, which normally is much closer to "free market" numbers than earlier arb years. I'm not defending the system, but it is what it is, and our players are getting close to "what they are worth" within the established system of setting the value of contracts for arb eligible players.
Pom's $8.5M was in his final arb year. Bogey's $7M is in his 2nd of 3 arb years. I think Holt was overpaid at $2.25M for his 2nd or 3 arbs years, but we're talking by thousands not millions of dollars under the system in place.
All in all, it looks like the Sox might end up saving a few million dollars over the estimates, but the Betts' arb decision might change that.