The points raised about Mileena's strength is on bait and whiff punishing is due to the fact that is how the character plays which is pretty much alien to everyone else who lives in 50/50 town.
Quite a few people say just block low and that's it but I feel it's the predictability of her offence is both a strength and a her weakness. Quite a few of her strings can be cancelled to EX Roll creating a 50/50 scenario mid-blockstring which is a risky but a good way to open people up.
I don't think she's low reward as her damage output is pretty good. Consistently dealing 30-36% meterless from almost every starter is good.
I feel Mileena is a fair character that is meter dependent to make herself really dangerous. Is she lacking compared to other characters? Sure she is and she has to earn all of her wins but I feel when played smartly she can be hard to deal with. Then again maybe I'm just seeing her through rose-tinted glasses and upplaying her