I think the current format is fine as it is. Maybe some changes to the seeding system will help, but on the whole it's fine. The problem with other proposed formats is that either you filter strong competitors out of the competition or you end up having strong team vs strong team every game. This sounds good but then the fixtures lose their luster. United vs Real for example is a fairly rare fixture, and as result every time they play it's usually special. I like the idea of having the big teams 'warm up' so to speak in the group stages to then enter a royal rumble in the KO stages.