I dont think giving flamers to rear echelons as there is already Assault Engineers (It would be heaven for Sprice) I reckon if people find the rifle flamers annoying you would have to increase its muni cost or increase the received accuracy on the squad who has that flamethrower equipped
I really like the flame changes and how they punish turtling, they got the numbers wrong at first(see kv8, croc, dmg vs garrisons, etc) but the spirit of the changes made for a better mechanic imo. That said I agree it's probably not a good idea to give flamers to mainline infantry.