...in city fighting... very very negative press...
What several of the posts above, including this one, seem to have missed is that it's not just a matter of negative PR when using flamethrowers in built-up areas. It's that the USA, as well as most other states, and all
civilized states, are signatories of CCW 1980 Protocol III. That severely restricts the usage of incendiary weapons whenever there is a danger of damage to civilians or civilian objects. Say houses that are not being used by the enemy, but that are adjacent to an enemy position. Fires spread.
WP rounds were used by US forces even relatively recently not just because that was an ingenious field improvisation. They were still available to troops in the field exactly for the reason that under Article 1.(b)(i.) of that Convention, they are not considered as incendiary weapons (their primary purpose is making smoke, not fire). So there was no concern against their use.
Incendiary weapons and in particular flamethrowers might still be useful, and not so restricted in use by treaty as to be impractical, for attacking, say, hardened military bases that still have air vents, shooting slits and the like. But at that point, a thermobaric warhead works on the same principle and can be a stand-off weapon. Bunker-buster HE warheads that perforate a good thickness before detonating and cause shock waves also work well.