Not sure what you are trying to say with the last part about the UCL becoming an actual league. With regards to the major leagues, I think they are as competitive as possible. The lower ranked teams get demoted to the lower division and the top ranked teams go to the Champions League the next year.
Edit: I agree with the disparity, but I don't think that in itself is a problem (except maybe Ligue 1). It would be like saying Tony Ferguson would probably beat most unranked LWs, but could get caught with something on any given day.
The top European leagues are not at all competitive. There are very few clubs that win league tittles.
In the last 33 seasons of La Liga, Real Madrid, Barcelona, Atletico Madrid, and Valencia have won 32 of 33 league titles.
In the 25-year history on the EPL, Man United, Man City, Chelsea, and Arsenal have won 23 of 25 league titles.
In the last 24 seasons of Bundesliga, Bayern Munich and Borussia Dortmund have won 20 of 24 league titles.
In the last 16 seasons of Serie A, Juventus, Inter, and Milan have won all 16 of 16 league titles.
80-90% of clubs have essentially zero chance to win a championship. And that is not going to change. In fact, the disparity is more and more pronounced as the payrolls of the top clubs grow disproportionately to the rest of the league.
The average salary of Real Madrid and Barcelona is 8 times greater than the median club in La Liga.
The average salary of Bayern Munich is 6 times greater than the median club in Bundesliga.
The average salary of Juventus is 6 times greater than the median club in Serie A.
The average salary of Man United and Man City is 3 times greater than the median club in EPL.
From a competitive standpoint, it makes no sense for these top clubs to play the great majority of the rest of the clubs in their respective leagues. To use your UFC analogy, it would be like a UFC champion defending the belt 50% of the time against a fighter outside of the top 10.
What I am saying is Real Madrid shouldn't be playing 38 matches in La Liga. They shouldn't be playing in La Liga at all, the only time they should face a club that has such a disparate payroll should be in Copa del Rey. Instead, they should be playing 38 matches in a super league consisting of clubs with relatively similar payrolls like Barcelona, Atletico Madrid, Man United, Man City, Chelsea, Bayern Munich, Borussia Dortmund, Juventus, Inter, Milan, PSG, etc. That way, almost all of their matches would be competitive instead of relatively few like it is now.