If you are ambitious footballer you don t make a step down club vise and league vise. You do it for the money. There is nothing wrong with that, but let s not make an unicorn out of a donkey.
Example was CR. He went from United to Madrid. At that time United was possibly a stronger club, but we can t deny that Real is a bigger organisation. Also La liga is at least on pair with Premier league and his brand
went up at least one level if not more. That s ambition. What Neymar did was not ambition, but i understand how a PSG fan would want to believe that.
It is ambition but he has failed and now he is dumb because he is trying to run away and go back to the "easy" route. As everyone knows and for the reasons you have pointed out, it is a lot more difficult (to the point it seems impossible) to win a CL with PSG. It is a very big challenge. Even Barça with Messi and lot of talented players has it hard.
Neymar had an "unconventional" path as he debuted in Europe straight in Barça and won everything there is (to the point he had nothing more to win there). He prolly though it would be an easy ride at PSG too and the money was good. Now that he has another experience, he wants to go back to his comfort zone. Usually, players start in lower clubs/leagues in Europe and finish at Barça/Real and feel like they have climbed to the pinnacle of football.
I'm not talking here as a fan of PSG cuz i don't like either Barça or Real. I used to only appreciate Atletico in Spain. I'm just trying to see it from his perspective as a player and human. As a PSG fan, even though i can comprehend his choice, i'll definitely erase him from my memory the moment he jumps ship.