Modded games allow for this, and even then the half track gets melted by basically any armour
Sure, but that's not the point. It is weak, it should die against basically any armour. But currently it is either you can reinforce your troops which is meh because in the heat of the battle most (not top 100) players are not able to micro refreshing everything at once, keeping your troops in cover and also keep your halftrack moving to dodge shots without making it turn 180 degrees OR getting flamers.
The flame halftrack currently has a very very short timespan where it is effective. If I build it then I do that to get Brits out of houses or to burn down emplacements. But usually at the same time as the flame halftrack is upgraded, the first AECs or a USF captain arrive. Against sovs it is useless either way because of their large squad sizes.
So if I have a flame halftrack that survived minute 10, I usually forget about it, because if I tried to burn anything, it would die in seconds because of all the AT inf and armor. But its other use, refreshing troops on the front (which is needed as Ostheer because of no front retreat points) is not possible once you upgrade the flamers.