Okay, so this is what I'm understanding so far...
Don't use Panzer Grenadiers because they are rather weak and the cost for the panzershreck upgrades price really aren't worth what you get out of it.
Don't use flame halftracks since they are too weak and get killed easily.
Don't use pioneers with flamethrowers since they are fragile and killed easily.
So basically, just always go for incendiary artillery and mortar half track doctrine? Is that what I need to do?
If it'd just a morat pit, use the above units.
If it's a mortar pit + Bofors,
A.)
ignore them and really pressure elsewhere and get tanks fast. He won't be able to help much elsewhere because of his investments in the emplacements and will be slow to get his own tanks as well.
Or
B.) Get help from your ally to double team it with paks mortars and flame pios.