the flamethrower was not touched. it does not down an enemy but simple an instant death weapon, so it depends on how fast it will kill people by yours and their connection. some Patches that affect connection and lag also effects the Flamethrower.
~ Billy, from Grim Adventures Of Billy And Mandy
I've used the flamethrower a lot since this game's launch. I can tell you this much: the flamethrower was definitely buffed at some point, it was nerfed recently, and now it's at a point that it's better than the first iteration but not as good as the second.
it has only been touched once, which was when they buffed its killing efficency. its lag patches that are affecting it. for example, when your opponet does not scream in pain when they are on fire but simply drops dead without being burnt and also shoots and downs you but after your down they just drop dead out of nowhere. that would be lag in the factor.
Answer = No
Still not fully answered regarding lagger detection, FT might be a victim of circumstance which makes it appear to be nerfed.
I used it for several months, it definately does not feel the same since the previous patch, reaction time to see an opponent go up in flames is very slow and often the FT has minimal effect. I have downed players using it on me with the Revolver while getting surrounded by flames only to lose 50% health.