Just to chime in here, as a longtime Diamond member, BR does treat it's top tiers pretty well. If you are concerned about the phone wait times, there is a special phone line for Diamond members that is almost always immediately answered. However, if you are flying business class on revenue J tickets all the time, I think there's not a whole lot of incremental value to be had there.

I work for an org that has an economy only travel policy, so where the Diamond status comes in handy for me is priority waitlisting of upgrading, which would be irrelevant in your case if you're already in the forward cabin.

DeltaOneFlyer brings up a good point also. Perhaps neither BR nor UA should be your program of choice. Choosing where to credit your miles for max redemption value doesn't have to go hand in hand with having status in a particular program.