I propose a much simpler, easier solution.
Lets just simply make the flamers of riflemen weaker. This can be done in the many ways such as
1) Reducing range from 20 to 15
2) Reducing the rate of fire of the rifle flamers
3) Something else
Keep in mind that this would not affect the flamers that assault engies , pios and other flamer units have. This would simply make the rifle version of flamers weaker. From a realism perspective , this also makes some sense, as trained specialists such as pioneers or assault engineers would obviously make better use of flamethrowers than general riflemen that are not trained in specialist roles such as flamethrower usage.
Meanwhile , penal flamethrowers need buffs, they are convicted criminals, they obviously know how to use flamethrowers well


