Spray tanks are simpler, lighter and more fuel efficient.Given one of their main drawbacks was their limitted range requiring operators to get rather close to what they intend to burn, I think those flamethrower drones will give the weapon a bit of a renascence. Probably less as a weapon per-say and more as a quick way to clear problematic shrubbery without endangering any infantrymen.
Incendiary munitions, grenades, bombs, rockets are even better.
Even then you'd have incendiary rockets.Butterfly away the thermobaric rocket. A thermobaric rocket, man portable or otherwise, fulfills pretty much the exact same tactical niche as a similarly mounted flamethrower does at much less weight, much longer range, and hence with much less risk to the operator.