To be honest it feels like the balance team at Riot don't even play the game themselves. It seems like they with each patch just pick some champions at random and roll a dice to see if the champion is gonna be nerfed or buffed.
Nasus is way too strong at this point. The buff to his Q has made him do far too much damage in the early and mid game. Before Nasus was a tanky bruiser that would scale into the late game, but now he gets his Q stacks extremely fast. Riot have given him all this extra damage without taking away some of his sustain. Champions that would counter Nasus before and make it difficult for him to stack his Q, like Teemo, do an insignificant amount of damage to him. And all the damage Nasus takes, he can easily heal back with his passive, which gives him an insane amount of lifesteal. Nasus simple has to press his Q on a minion and then he is full health again, and the healing just gets stronger and stronger with the extra Q stacks. Furthermore, his W as a way too strong slow compared to its range. He can easily press his W on his lane opponent and chunk them for half of their health with one single Q at 12 minutes in. His E also does a significant amount of damage without building any AP at all.
It is extremely difficult to prevent him from stacking his Q as he has extreme sustain in his passive.
Over all, he gets too strong too soon in the game. And his Q stacks up so fast that he does not have to build any damage at all, and he can use all his gold on building health, resistances and utility making him practically unkillable, while still doing insane damage.
Nasus is just one out of many champions that makes the game not fun to play, resulting in an extremly toxic playerbase. It really just ruins the fun and makes League a frustrating game to play, when the balance team has no insight in the game.