He is harder to play, but it is due to several indirect nerfs. You probably simply need to improve a bit as Nasus as well since he is a champion that at the moment can't afford to make a lot of mistakes in lane.
Nerfs to movement speed items, the strength of adc items, nerfs to some items that he commonly built, the mastery changes (for the most part didn't help him), and the pacing of the game have all hurt him.
The amount of CC in the game is pretty high with recent champs having CC heavier kits. Rylais buff are really hurting him when he groups and lowering his ability to escape.
If they provided a bit of buff to his base stats I think it will help him get closer to 50% again. He was around there at the start of the season but has fallen as the season has gone on.
Learning him requires patience and understanding when he power spikes. After you get mechanically good with him, you then need to get good at making decisions. Mistakes in decisionmaking as Nasus (when to splitpush when to group when to rotate etc) are really really important if you want to win with him.
That being said. If you learn how to farm with him under pressure, not die in lane, and get good at making decisions then you should start winning more games. I almost exclusively play Nasus and I can still win games in higher Elo, but my decision-making got a lot better. I do think Nasus is harder to play than last season.
Edit: I looked at your builds. They aren't that good. He has a very precise build for matchups. He only builds one damage item and its either
or
and then full tank.