Neymar was absolutely brilliant for PSG when he arrived up until his ankle broke. He got surgery, tried to come back for the world cup, didn't really work, started to get better again and then he broke his ankle for the 2nd time, that's when things started to go downhill.
Not really no, he won the WC in 2002 when the big star was obviously Ronaldo. He played in a insanely strong national team at that time compared to Neymar's. He was the star in 2006 and was blamed for his bad performance when Brazil got eliminated by France. He only was the star for Barcelona for 1 year and a half (when he was brilliant).
Flatlined is a big word, he was the best player for PSG when we beat Bayern last season in the CL quart finals. He also got the best player title along with Messi this summer during COPA.
Ligue 1 isn't the best league in the world, i'll give you that.
He could have had this easy lifestyle everywhere. Actually, the birthday/carnival stories come from his time at Barcelona, he didn't do it at PSG. Look at Dembele showing up late half the time at practice with Barcelona, Bale with his golf, fatty Hazard or Asensio partying at Real Madrid, expensive players can do pretty much whatever they want in almost any club.