They took the two literal hottest available properties in the world in succession for, what, €367,000,000? And added that to Cavani for what was unarguably one of the best strikeforces in the world, on paper, at least. Verratti, Thaigo Silva Marquinhos (rated higher then than now), Di Maria supplemented with Motta, Alves... you're not going to sit here with a straight face saying that team were not expected to do great things, are you?
The whole point of assembling what they did was to take on all-comers irrespective of when they faced them. In hindsight, it hasn't worked out, but the prevailing thought then wasn't that this was a quarter-final level side - if not par with those expected to win it, then certainly not far off, at all.
Not sure about your last paragraph, as you're entitled to your opinion, but I think a player like Neymar needs the majors and the CL far more than the league, whichever that is because he has always been touted as one who will be an all-timer and all the rest of it - glitz and glory on the grandest stages. If PSG had've won the CL once or twice during his time there, the status of the league would have been elevated... imo, at the very least, being in Ligue Un wouldn't have been held against him.