Nasus may be easy to play but he is very farm and item dependent to change from a liability to an asset
His farm needs to be at least consistent to have a good mid to late game, his early game isnt very notable
Building him correctly is the biggest issue with nasus, due to how expensive his items are
im not sure about the point that he dosnt fit into many team comps, this is untrue, he fits into many comps becasue of what his role is
He can initiate on an over extended player with wither
He Anti-carries extreamly well (one of the best other then malphite)
A proper build allows him to tank extreamly well along with his life steal passive
Hes a great AD champ considering how his spirit fire reduces armor, his ult converts aoe damage into ad, and by building a black cleaver on him, you will be doing bonus damage on top of true damage with them having no armor
Nasus does many things at once, and is extreamly well at them