Doctrine is what is taught. In that respect the FMs are WHY something needs to be done and the some explicit guidance as to how.
IMO, the "manual" should form the reference work from which the teaching is done and not aim to teach something in and of itself. You cannot throw "Infantry Platoon Tactics" at a 2nd LT and then assume he is good to go.

The biggest problem I have with the current US FM's is the poor history, and some of the worst writing the English Language has ever been subject to, in terms of wordy, complex, high-falutting gobbledegook.
Clarity of writing IS clarity of thought. - anyone with any doubts, look at the drivel that gets written about Operational Design.