Battlefields are highly path dependent (lose 50 men on one hill - combined with unreplaced troops on the previous one - you've just lost 10km^2), chaotic (that shell just randomly took out your battleship during a beach rush - no more covering fire - you get slaughtered), subject to the influence of volatile human psychology (sounds and sights can decimate morale, focus and the ability to shoot people in the face at random times), resources (platoon 3 runs out of ammo, bogged down on critical hill - backup platoon can't get to them - out of range of covering shelling - lose the hill and the valley), weather (it's raining - they have tanks and relieved troops), positions (your hill just turned to mud and blood), communications (platoon 1 - decimated - incoherent babble and screaming, platoon 2 - nothing, platoon 3 - incomprehensible, platoon 4 faulty intel) and hell - wind direction (dust blows into your platoons' eyes - but not into the enemies).
None of that has much to do with the general on the ground - it's just shit that happens in highly chaotic, unpredictable, uncertain and resource constrained environments.
I see the same kind of criticism leveled at CEOs.
Granted, many of them are complete morons and can drive companies into the ground. However most are simply doing what appears reasonable at the time, and are just unlucky not to have the corporate/economic/technology winds (or dust) at their backs.
People overrate what people can honestly achieve in highly chaotic environments. 15% of corporate CEOs are replaced every year - notice how companies don't change much from year to year though - I have. However, changing often definitely let's us lionize the lucky ones (see hedge funds, startups, novels, movies, tv shows and any other at scale, highly path dependent, chaotic and random systems).
We failed in Iraq and Afghanistan because we needed 10x more troops on landing and about 15x more resources and a great deal more international support.
This is by far the most predictive of success on any battlefield (and business) - irrelevant as to who is actually running it.