I say the spring shop guy probably knows a lot more about that than I do, or at least I'd hope he would. If he says one leaf is about right, I'd go with that.
I have no complaints about the air helper springs on my motorhome, though obviously you're not me. I see no reason nor need to let the air out for leveling; I just level with them set appropriately, which presumably also helps a bit in stiffening the parked motorhome against bounciness as people walk around etc. Maybe once every few weeks at most they require a touch of air.