It's definitely principal agent problem all over. During WWII I think it was clearer politically because the military grew over 10x from the 30s to the peak of the war effort, and the massive budget windfalls there were extremely tempting to take advantage of and extremely egregious when called out.

Now we're in a society of permanent volunteer military readiness, and we have to deal with endemic problems. The corruption and solutions both look different, and solutions have to have sustainability in mind.

I think you might be right, that Congress right now does spur on overspending rather than underspending. It's just about impossible to close a base anywhere, from what I hear. Still, in the long run, I do think it's better that Congress keep control of this and have continual oversight. I think it might be better suited to the Senate, and I think it's better suited to committees, but there does need to be a accountability there that is entirely outside of the military.