I dont think Muscala is a 4 at all in the NBA. He cant guard 5's either but he gets embarrassed when he has to chase 4's.
The only time Muscala can pass for 4 is when he's out there in those 3rd/4th quarter mins with all 3 of Jimmy/Jo/Simmons.
But he also gets embarrassed when opposing centers just back him down and shoot over him.