Kagehoshi, fire can be equally as dangerous. The fuel used in the weapons to take down these suits would not be your usual yellow flame it would be blue or white hot and clean burning making for a very deadly weapon. Keep in mind that flame throwers do not need air to burn they just need a flammable gas which is what would the flame thrower would be shooting to create the heat to do the damage. Plasma would also create a different image entirely than flame. The psychological factor is very important for the flame thrower, seeing that stream of flame is crucial to create that effect. Seeing a stream of plasma for the first time would confuse people to the point that they may not even understand what just hit them; which is not scary it is just aggravating. And on a planet with atmosphere you would see a giant stream of flame anyway because it would instantaneously ignite the air around it hiding the plasma from view. The damage would be something along the lines of an assault rifle just continuous and with lasting effects when not even being directly hit. The point of the low range is simply because it is difficult to project liquid fuel long distances. The spread of the flame thrower should be a fairly small cone only about a meter or so on the outer edge of the weapons range making it comparable to a shotgun but not nearly as large of a spread. If anything a flamethrower would be a Minmatar style of weapon, plasma could be Gallente, Amarr and Caldari could find their own versions that do effectively the same thing.