From my experience most standard forks don't have enough damping so talk of them being over damped is not what I've felt. The harshness from adding extra on the dials is more due to the design of the damper and the lack of ability to flow oil without spiking transferring too much feedback to the rider. I've had dampers modified to remove this harshness and generally I'll up the pressure after this as the fork has started to function correctly (or close to).
Another reason for guys running lower pressures than recommended is to do with tight bushings. Zeb's are commonly tight. Rockshox put longer bushings in these and with their usual inability to hold tolerance in production forks they have ended up with a heap of forks with tight bushings. Get the bushings sorted and the damper modded and the Zeb isn't a bad fork.
Then put on a Secus and it helps with the progressiveness. As usual...just add $$