nasus is a maokai counter in the same way that he's a counter to most top laners, ie that magical late game outscaling
of course most people wouldn't know how to put in the work to get there as nasus doesn't naturally outscale like other champions tend to do late game (trist).
shut him down and he never will.
xerath is also strong against yasuo, as his windwall is on a long CD and only blocks one of his abilities. by the time yasuo is sliding in for Qs or autos he's in range to where his wall cant really block the stun either.
Trouble with Nasus is you have to rely on your team not to royally fuck up for the first 20 minutes.