The doctrine got plenty of use before heavy tanks were buffed into space and picking anything else but grand operations became a meme
Are you joking? Do you have any idea how strong heavy tanks were a few years ago? Have you played Tiger ace when it came out? They were not game breakers, they were session enders and made people ragequit. One single Tiger ALONE, without any support whatsoever, could clean up an entire game. There was a tourney game where I think Luvnest lost every unit except for one or two pioneers, and still won because he had Tiger ace.
Even if you would buff the flamehetzer, the rest of the doctrine would still be ass and forbid any use in a competitive scenario. It's a classic meme doctrine. It has too obvious weakspots, is too obviously countered by almost any meta build.
Pretty much every ability in the doctrine would have to be replaced/buffed in order to be useful, sans Opel.
So, are we now at that point that we can say that KV8 is op?
The KV-8 used to be bugged, which made it have 2 flamethrowers. Each flamethrower was also much much more effective than they are now. Then it was super overpowered and pretty much an instant win whenever it was called in.
Now however, it is rarely seen, despite being in a considerably better spot than Hetzer, which only reinforces the trashy-ness of the Hetzer, never being spotted at all.