Honestly with the type of midfielder that real Madrid lined up today I am not surprised that they lost. Yes it understandable that they coach is also trying to have a solid team for their match against Athletico Madrid in the mid week but going by how solid Real betis has been lately I will say that they underrated then too much and they paid fge costly price.
The league is still very opened and with inconsistency here and there between the top three team, the league is very open for anyone.
In my opinion, Ancelotti made a mistake in playing the line-up and another factor is the large number of injured players, which made it difficult for Real Madrid to maintain their best performance. I also saw Mbappe was not on fire, Bellingham was also suspended which could affect the attack and the defensive area was not well defended after they took the lead.
Maybe Ancelotti is preparing his players for another game vs Atletico in UCL, but if Real Madrid players continue to play like this, Atletico will punish Madrid with a big score.