In the midst of a tough war you don't criticise your leader, Gort never came out and accused Chamberlain of all kinds of failings, Wavell never criticised Churchill for denuding him of men and materiel on the point of victory never did General Mark Clark (of all people) attack Churchill for the third battle of Monte Cassino.
If Machyrstal has a problem with the war's direction (then I think he has a point) he should do it in private, he perhaps should have ready a proposal for a change in tactics, perhaps by garrisoning the area affected and having rapid reaction airborne units to cut off the retreat of guerilla groups.
Instead of marching up to a compound, have a fir fight, win, leave, and then do it all again six weeks later.
Taliban will fight an attritional battle happily for years, they only dploy in tens and fifteens, we deploy in twenties and thirties with hugely expensive equipment, theyhave Kalashnikovs, a thermos and a yashmak.
Do the math.