I think we just need to go horses for courses with Soldo.
He has shown, more than once, that he can nullify the high quality rucks of the competition (Gawn, Grundy) in a way that Nank can't. But up against a battler like Ceglar, Nank is clever and crafty enough to turn his abilities (and even literal shortcomings) into an advantage.
I hope we do try both at some point during the year. Soldo is actually a decent option to fill a hole in defence, and has taken a few intercept marks doing so. So we can float him between there and first ruck, while Nank can float between Ruck and forward (or even winger if we want to go left field - again, literally). We don't actually know whether it will be worse in the shortened quarters or not, I think it's worth the test.
But if we're coming up against one of the undersized, or less impactful/dangerous, ruckman, and we only want to go with one ruck, Nank offers more.