This is how myths start. Someone says it once, few people repeat it and then it becomes common phrase which is more or less BS. Yes, you beat what is in front of you
but it is huge huge thing if you avoid big guns.
For example; you played tough game against Atletico. 3 days after tough game against Pool, you needed to play with best 11 in high tempo game and in game with dozen dangerous tackles. Liverpool played "easy" game vs Benfica.
On weekend Liverpool will be on 100%, City will need to rest some players. That will happen again in semis. City will play with best 11, Liverpool will win in first game already. Also, despite Villareal beating Bayern, in 4 games of 5 Bayern would win that tie. Don't tell me that you think that Villareal now is better team than Bayern? Ffs, even we beat them this year
.
Look at your path in cups last few years. First few opponents were championship/div 1 teams where Pep could rest nearly whole first 11. On the other hand, when you get Arsenal, Villa or Spurs away, you can't rest players.