I have read both, and Foucault is 100x the charlatan than diamond is. Foucault is responsible for significant amounts of fashionable nonsense within the academy.
To apply that to Foucault and and Diamond, Foucault explored complex ideas obtusely and Diamond explores dumb ideas simply.
Sure, the academy has a bias towards complexity. It is slightly self-justifying. But let's not be black and white thinkers and assume that the opposite is true, and that airport reading by somebody with no historical credentials must be some secret truth the academy doesn't want you to now. It might just be popular bunk.
If you believe that critiquing the prison-industrial complex is fashionable non-sense, then I think I know where you lie politically.
Lacan, Zizek, Foucault, and Derrida are The 4 horsemen of the epistemological apocalypse.
We should probably just go back to Rhene Thom and Morphogenesis, except that even that theory has lost face. A hundred years of denying the importance of Hegel's Logic has led to a significant loss in the progress of human civilization.