So basically we would have to ban Liu, Mileena, and Jax. That's an idea. I think it would still be very challenging for people to beat the listed players if they randomed, while the challenger picked anyone but the top 3 characters.
The overall idea boils down to this
Random = Ain't nobody got time to play months just so they can random select some pro and still lose
No horrible matchups = People got a chance, newbies in particular can have an easier time playing vs someone and learning the game
Free pick= No newbies attracted because it's too easy to counterpick
I'll say this though, there is no reason to offer giftcards if you're gonna make this
A) Public instead of refering to a particular MK community
B) Unwinnable by noobs who may or not be interested in the game
If anyone is gonna beat these pros it will be someone with actual fundamentals and backed up by a good matchup, no fundamentals, no victory. Fundamentals also mean that person plays fighting games and that's the audience OP is looking for, noobs will have a hard time winning even 9 1 matchups and are mostly casual scrubs.