All the effort and time to get through all 300 challenges and what do you get? A trophy... and a mileena costume.... annnd? Is that really all there is to it? I like challenge tower a lot and it brings something to do once you beat the story and beat the arcade with everybody but there's no payoff. I'm long past the age where i want to see scantily clad women in a video game, if i want to see **** I'll just google it, besides mileena's costumes are already scanty enough I dont really need to see her wrapped in a rope and have her giant baraka teeth on display. after knowing what the challenge tower gives i really dont see the reason continuing with all this effort
The reward does suck, but it's something to do. Challenge Tower adds a lot of replayability to the game. Some of them are really fun to do. For example, I got a test your luck where I had unlimited super meter (or whatever it's called) and my opponent couldn't block, so it was fun spamming my x-ray lol. However, some of them are really really difficult and it often feels pointless to even try beating it, because as you said, all you get is an extra costume.