Up until WW1 infantry battalions weren't internally differentiated nor was there much external differentiation. They were all formed bodies of disciplined soldiers broken into 8-10 companies. They would be trained to dismount from boats, ride camels or horses as the case required. Cavalry troopers were trained to fight dismounted with the same weapons the infanteer used. The whole army morphed to suit strategic, operational and tactical needs. The same Army fought Metis, Ashanti, Zulus, Pashtuns, Boers and Germans and the Mehdi's Armies at Khartoum and Omdurman. A long service Sergeant at Mons in 1914 could be expected to have operated against all those foes using all available transport performing everything from crowd control and ceremonial duties to patrolling and high intensity, industrial warfare.
Bring back the generalist.
Nice in theory, but more difficult in practice.
That worked in the post Brown Bess, pre-Maxim days when you didn't need formed and drilled mass formations like you did with muskets (which required specialized training for the Infantry) The brass cartridge rifle made everybody into a skirmisher. The only weapon systems you had were rifle, bayonet, grenade, sword, and pistol - so everybody not Artillery could get the same basic training. Tactics could adjust to fit the local situation, but weapon systems were static.
That ended in WW1 with the invention of first the machine gun, then later the tank. You get weapon systems that are overly complex and specialized to teach to everybody, and that trend has only accelerated since.
Now we have C7, C8, Pistol, Grenade, M72, M206, C9, C6, M2, Carl Gustav, 60mm mortar, Eryx, TOW, 25mm chain gun, 105mm and 120mm tank main guns, shotguns, 2 or 3 sniper rifles... that's just off the top of my head. There's just too many weapon systems to make everybody proficient at everything.
And the turret stuff has a whole slew of supporting equipment and FCS to cover. It's not much of a stretch between C9 and C6, but there is a big difference between firing the C6 off the bipod and firing C6 as the coax weapon out of a Leo or LAV.
There's also a big difference between the employment of weapon systems off vehicles vice employing weapons with your boots on the ground. The division of the combat arms into Infantry (thems that fight on their feet) vice Armoured (thems that fight from a vehicle) makes a lot of sense from a training and employment perspective.
Where I think the "mistake" was made (if you want to call it that) is when we started putting Infantry Sgts and MCpls into vehicle crew commander positions (especially turreted vehicles) and started requiring them to pick up the "Armour" skillset of fighting a vehicle *in addition* to their boots-on-the-ground section commander role. That's too much to absorb, and you compromise one skill in favour of the other.
I don't know why that happened; my history isn't that good. Maybe the Armoured Corps may have turned up their noses at a job that wasn't tanks - if so, shame on us! But it doesn't really matter anyway. Better we learn from the here and now and put in a here and now solution:
Give the Armoured Corps the LAVs (and all future APCs) Driver, Crew Commander, and Gunner (if there is one) are all blackhatters. Let the Infantry concentrate on the Infantry tasks instead of being spread so thin over such a wide skillset.
DG