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 managed to make a surprise after successfully qualifying for the quarter-finals, but their chances of advancing to the semifinals are very small because they will face PSG who managed to eliminate Liverpool through a penalty shootout. Real Madrid once again showed its class as the most successful team in the UCL, surprises like this always happen in the UCL even though several teams have performed consistently in the domestic league.
Next, Madrid will face Arsenal, I don't think it will be too difficult for Madrid to eliminate them.
Aston Villa reaching the quarter-finals was not based on sheer luck, but because they played better than their opponents. It's just that they have luck in other things, where they only met small teams (Club Brugge) in the last 16. From the start they already had the advantage in power and team mentality, so it is very reasonable if they can win the match and qualify for the next round. Maybe the story would be different if they had to meet a team that was equally strong or far above them, and I think this is what happened in the quarter-finals, where Aston Villa will face a strong candidate PSG.