How often do you ride? With only 600 miles on the Brooks, the saddle wasn't even broken in much less your butt. If you don't ride often, then your butt won't like a road bike saddle.

If you are doing short commutes, then a road bike IMO really isn't the right bike. Many of us that ride road bikes a lot will be comfortable on a road bike for commuting. But if you ride infrequently and then do several rides all at once, your butt will make you pay.... in saddles.