First, the Wehrmacht already has at his disposal the mg-42 rack (best lmg in the game and has one unit with x2 flamethrowers) and secondly, i think, this mod doesn't balance around historically accurate facts, just gameplay wise.

The goal was to give all factions diverse and fun tools, but not really the same tools. The Wehrmacht has the unique grenade launcher instead and the Urban Assault Panzergrenadiers is specially designed around flamethrowers.