AT is not look like medic, in Wehrmacht and soviet you skip AT too. So when you needed you can go back tech.
As Pip says, its look like for USF you can only buy the ambulance if you go Lieutenant.
But it's not. As okw you sre the only faction that starts with healing. You get 3 aoe crates, you also get self healing on multiple combat units (volks need this returned to vet3 however). Doctrinally you also get single crates on the 221 and ambulance like opel blitz.
Okw is extremely aggressive. Part of the trade off for this is either economic drain on healing or certain teching.
In a similar vein soviet squads are extremely durable, part of the trade off for that is large target sizes and only being able to heal in base while all other factions can heal on field (there are doctrinal exceptions however, like there is for okw)
I could absolutely see okw getting a pair of medics at base when medics are unlocked, but medics being in the medic truck is part of their design and removing that aspect could have unseen effects.
Look at it this way, both med and mech reduce bleed. Mech does so via unbleeding armour, and med does so via healing. One is offensive and one is defensive.
Returning volks self heal to vet 3 could be exceptional for helping with the feel of okw healing. They don't insta vet via shrek anymore so there is no reason for it to be so delayed. Okw was designed to function regardless of truck. It's just been nerfed out of them in the name of homogoniziation