Irrelevent.
First, the Champions league involves much more teams (i'm not just talking about the squads who actually play).
Second, the teams which are engaged in this compe ion all have other compe ions to deal with (national championship and national cups)... It can be very difficult for the best teams to focuse and deliver in every compe ion they're involved in.
Third, the Champions League exists since 1992. Before that, it was the European Champion Clubs' Cup. It was not just about changing the name of the compe ion. I'm not gonna explain how and why but since then, european clubs soccer has become a huge and very attractive business without any common rules nor any limits.
Therefore, the richest you are, the better you get (the best players go where money is). As simple as that.
And with the arrivals of Russian billionaires and Emirates princes, the situation has worsen greatly.