That of Aston Villa reaching the quarter finals is not luck, because they humiliated the club that they played with in the round of 16. A narrow escape is what is called luck. Liverpool winning PSG in the first leg was based on luck. PSG qualifying through penalty and Real Madrid are what we consider as luck. You shouldn't also use the performance of a team in her domestic league to judge their performance in European competition.
Aston Villa should be considered a team that has the ability to qualify for the last eight because if we look at the aggregate with Club Brugge, of course the difference is so big that this is not worthy of being considered luck, but it is more worthy of being said as a fairly pure ability from Aston Villa itself. As for PSG and Real Madrid, it is worthy of being considered lucky because the opponents they faced were quite strong opponents this season, so for Aston Villa it should be considered different in this kind of thing and what you said is true.