It could be cool to have reinforcement feature as "normal" player (not AI) in battle generator. Now you must think carefully what units to choose before battle. I must confess that I choose too much tanks often (maybe I hate losing battle to AI)... So winning is too easy that way. That's why it could be nice to "share" some tank units into another later phase of battle (let's say turn 12 AI will add 5 tanks and so on)...
You as a human already do - simply leave the reinforcement troops by the baseline for later use.
It definitely makes life interesting sometimes... Of course, if there is a big force discrepancy (like the JT example mentioned), AI cannot do much about it, but when you leave a depleted company (by now almost down to platoon strength) to guard an objective cluster and suddenly a fresh Pz III platoon appears...