Illusion for me: 90% of the songs are just the girls singing/rapping fast. Repetitive verse and weak chorus. Less vocal part and quite boring.
Girls: Ngl, I feel kinda cringe with all those Kwangya references but this song still suits better and stronger as the TT than illusion for me. The pre chorus, chorus and post chorus verse are very catchy and they served more vocals in this song compare to illusion. If sm rearrange this song with less rap part and removed all those Kwangya thingy, it would be such a really catchy song.
In short, I don't know why many kpop fans like illusion more than girls. I understand people's preferences but I still don't understand why, lol.