how hard is the champion league

It all depends how much the players in your group play. You could advance from champion to legend with about 500 points (again, it depends on your group) which is about 55 blitz wins or about 8 wins a day for 7 days.

Either way, paying attention to leagues is the wrong idea if you're trying to get good at chess. it's just an achievement chesscom uses to make players who play a lot feel good about themselves, even if they haven't played well or improved.

Thanks a lot btw I was trying to get to the champion and finish first to advance in (legend) that is the last league because when you get there you can join a special club which is made by chess.com and also join prize money tournaments which occur in the club

I am trying to get better at chess and I play multiple rapid games daily because bullet is not good for improving players