Real Madrid performed poorly in La Liga last season but played well in the Champions League, losing to the reigning champions in the semi-finals. So it may happen that this season they may do well in La Liga but poorly in the Champions League. We have to wait for the group stage and see how they perform.
Before the group stage begins, it is indeed difficult to determine the strength of a team this season in the Champions League, even though the domestic league has already started. And even though the domestic league has started, it doesn't mean that what you see now is the real strength of a team like Real Madrid, because it could be that in the middle of this season, Real Madrid has another strategy that they didn't apply last season, so they might be stronger. Because it's still not certain that Real Madrid can be stronger in La Liga, but it could be worse in the Champions League, even though for now Real Madrid is at the top of the La Liga standings after wading through three matches.
You have a good point here mate,the performance of a club in domestic league shouldn't be used to judge the club's performance in champions league because it isn't a domestic club that they are used to playing with and for that reason they know the weakness of almost all the clubs in that league.
However,I strongly believe that Real Madrid will try their possible best to make show that they perform better than last season in the Champions league this season. This is the league that they are more after and not the Laliga but we can still see that currently they are the top on their table and this will make them more focus on coming up with a strategy that they can use to go far in the Champions league.
After all, in an assessment it can't just be about good in the domestic league and bad in the Champions League and vice versa, and then compare it to last season for this season. Instead of thinking or judging in that way, why don't you judge and put more definite hopes on Real Madrid this season, like for example about doing well in all competitions. Because after all, Real Madrid is a big team and of course, Real Madrid has good quality and ability to get a treble winner and not only about Manchester City.