I dunno; at some point you gotta take a look at all the money that's been thrown at it fixing it and reevaluate.
Another thing you have to do is consider how you're fighting; e.g. flamethrowers wouldn't be a very good method for infantry room-clearing because the house catching fire and trapping the rest of the squad would be too distinct a possibility, but flame-throwers would be very good at clearing trenches, bunkers, and [dry] grassland. (Ignoring the possible political consequence of using flamethrowers on civilian populations.)
After the flame thrower hits the room, you no longer need to clear it. In Fallujah it would have been a nice tool. And in those mud huts in Afghanistan. The only downside is that they really are extremely dangerous to operate.
RE Retrofit:
The thing is, the uppers already exist and are produced by a number of companies. It’s an easy swap, the guys are already trained on the platform, the ergonomics, mags, and ammunition don’t change... it runs cooler, runs cleaner, and runs better.
It would seem, on the face of it, to be more cost effective than developing a new firearm to replace it.
And like I said - it works. Look at the AK47 and it’s myriad variants. Piston drive is the way to go.
RE Flamethrower:
I would never, for any reason, want to strap one of those bombs on my back. Every rifle in the area knows who and what you are and what it will do, and will concentrate absolute ballistic HELL on you... those WWII guys had serious brass balls strapping those things on, for sure.
But you are correct - it was/is an awesome and terrifying battlefield weapon. I believe they had them on tanks back in WWII, also.
I recall the USMC formally requested to use flamethrowers in Fallujah, but were denied...
One can only imagine the glee of Al Jazeera filming that...