Yeah. You are right. Buying some talented players means a club wants success in any competition they are in by the time they buy that player, and I think other clubs need this too, although, as you said, it is true that the Champions League is also a tough competition and not all teams can endure the pressure in it. That is why you will see teams doing very well in some leagues, but when it comes to the Champions League, they find it more difficult to shine by having some tough teams here with talented players than we think.
You cannot guarantee or be very sure that PSG will not repeat that mistake again. You already said that these competitions are tough leagues, so therefore, in the next season, we should not put any hope in any team yet till we see them succeed to the final stage of the competition. So PSG, I think losing to Bayern Munich is a mistake, but Bayern's squad is stronger than theirs, and that’s why it happens that way.
But this begs an important question: does PSG need talented players or does PSG need players who are fully ready to rumble with the best of the best in the Champions League? They have tried different approaches over the years now to finally lift the Champions League trophy, but maybe building a young team that is hungry for titles would be a superior way to give their hope another shot. They did all kinds of stuff now and nothing worked till perfection. But now they are running out of time because once Mbappe leaves, the club isn't as great anymore for other players as well.