In my opinion, what's "wrong" with the CL is that there aren't enough games between Europe's best teams. If you're one of the highly seeded clubs, you can go from the first game of the competition to the final and face about three other big sides on average. Four would be the literal maximum, if you got such a nightmare draw that you faced a top team in every round of the knockout stage, or if it's one of those years where a club like Barcelona ends up on Pot 2 for whatever reason. Point being: in the course of crowning the champions of Europe, so few games are played between the top clubs.
Odds are that at least one or even two of the teams you meet in the four knockout rounds would be someone punching above their weight, like Porto or Leipzig. And if you go out in, say, the quarter finals, you can have a year where your club literally just doesn't play against any other big team in Europe despite getting more than halfway to the final in terms of number of matches played in the competition. And while it's statistically unlikely, a club could win the whole tournament without facing a team that has ever won it before or would currently be considered realistic candidates.
In the 2017-18 season, Liverpool's journey through the Champion's League pitted them against Sevilla, Spartak, Maribor, Porto, City, Roma and lastly Real Madrid in the final. A grand total of two legitimately "big" ties throughout the entire span of the tournament. While they didn't win it in the end, they could have been crowned champions of Europe after facing only two other teams that were realistic candidates for the trophy. They won only three of their six group games, two of which were against the team that finished with zero points. The next year, Liverpool won the trophy after once more getting nine points in six games in their group, having faced three big teams from start to finish (PSG, Bayern and Barcelona), with a final against Tottenham, the sixth biggest club in England. That's not to single out Liverpool specifically, it's just a good example of my point. It's not enough of a test, in my eyes. I want the champions of Europe to have proven that they actually are the team that should be considered if not the best then at least equal to the best.
Meeting so few of the top teams throughout an entire competition is fine in a domestic cup. We don't regard the winners of the FA Cup as the greatest team in England. If I'm to consider the CL winners to be the actual champions of Europe, I want them to face most if not all of the other teams that can feasibly compete for that honour. Certainly more than two, three or four. As I pointed out in another thread, Barcelona and Bayern are widely regarded as the two greatest teams of our generation, yet they've met a grand total of three times in the last decade: 2013, 2015 and 2020. I think that's a shame. While I wouldn't necessarily demand that they play every single year, I think it's fair to expect more than three encounters per decade between Europe's top clubs.
I don't want that to be accomplished the way the ESL wants to do it, with their ridiculous concept of "founding clubs" and the upheaval that they're causing in the football world; but I certainly can't deny that I've been hoping for something new and innovative to happen in European club football. I've never felt like the CL was enough on its own, and that's not just because we've barely been in it since SAF retired.
I want more football between the best teams and players, but I didn't want it to happen this way.