Seriously. They all have the same buildup/progression/instruments/what-have-you. The only ones that were remotely interesting were Draven's (different instruments, chanting) and Diana's (vocals, the lyrics were interesting). But both of these still followed the same template of quiet repetitive dun-dun-duns (regardless of instrument) then a buildup to the same boring progression. And finally, a big ol' chorus of violins reaching a crescendo then suddenly stopping. This is not actually intense.

Please compose different champions' themes in different styles. kthx.

There are songs for champions?

That's because all of the champion login screen themes are based off of the main LoL theme.