The thing about DEN's scheme is you can get away with a lighter Mike than most 4-3 defenses due to the way they protect the Mike with the DT's.
That's why getting a real MIKE is so important tho. I don't think this is the scheme they want to be playing, I think it's one they are forced into because the MLB position is so incredibly bad.
They'd love to create more pressure up the middle by stunting those tackles and mixing things up a bit more. Until they solve the problem in the middle, they can't.