I don't think you can call a prop firm betting against traders a scam.
You go to a casino to gamble, it is in
casino's interest for you to lose. But you can't call casino a scam.A scam is something they hide truth from you, and mislead you.
Also if you research what MFF offer,that they lower their fee significantly lower than their competitors, make drawdown higher and profit target lower, give free extension and unlimited free retries , and offer 112% fee refund and bonus when you pass challenge; why they do all these unless they really hope traders to pass challenge.
I really doubt MFF can profit with all that terms if all they do is to bet against traders.
They must have figured out a way to sort out who are winners and who are losers. So their system can bet against losers and follow winners, to benefit not only from their losing traders but also their winning traders. Only they can do this that they can offer so generous terms that beat their competitors by a huge margin.
Suppose they have 1000 live accounts traders, out of them MFF decide 20 are consistent winners. They could put one million to follow each trader, for a total of 20M trading capital, they can profit huge on these winning traders.
If they can do this, then the more traders pass challenge, the more profit for them.