We all have complained about the fact that Ao100 needs more variety. But not the variety makes this challenge worth BLADE difficulty rank. There is a phrase about more enemies after level 25. But we all have seen that that's not true. And it should not be true, because having around 25 Viles and 50 Revenants isn't completeable at any case.
I propose buffing monsters up dependant on your current base level. For instance, former human at level 50 would have twice as much HP, +1 accuracy and carry 40 bullets to compensate. And other enemies would have something like this. With this, levels after 25 wouldn't just be as normal ones, while marine slowly levels up his guns, but will get harder and harder. To keep this partially fair, monsters should drop more and more ammo to prevent it from becoming as unfair as 25 V's + 50 R's.