There are a few balls that are weaker than the Rhino, that are potential drop-downs from it. I have the Rhino and I use these.
1. Storm Tropical Storm Hybrid.
I like this as an option better than the TS Pearls for 2 reasons. A) it is a slightly stronger coverstock; so it picks up earlier than the pearls, and, B) it has a less flippy backend, which helps control the dry backends. It still hits plenty hard for such a ball. It needs a strong drilling and the differential is very tiny.
2. Hammer Blue Hammer (the new, current one).
While this is marketed as urethane, it is truly a urethane/resin blend. I have NEVER had such an easy coverstock to change with both abrasives and polish. It clears the heads so easily, it is easily a 1/2 to full step weaker than the Trop. Storm Hybrid, I mentioned above. It actually needs the dull 4000 grit surface that it comes with. Otherwise, it would be only a spare ball, it is that weak. Meanwhile it has a decent backend, very un-urethane-like. It should also be drilled strong, not because of the weak core (the differential is still lower than average, but much more than the Storm ball) but because of the weak cover. It is almost ideal for playing down and in, eve for someone who is rev domonant, like I am.