Understandable, there's a lot of unexplained mechanics that mostly mirrors the early advance wars series.
The enemy's medium tank does stupid amounts of damage and is a bit resistant to most of the units the player has. You'd have to take advantage of the fact that the attacker gets to deal damage and reduce the defender's unit strength first to beat the MdTank. It is possible to finish this map with no units getting wiped out.
A few of the people who tried during the jam managed to only have 1 or 2 units die too. These guys are the ones that had some familiarity with the advance wars series.