Unfortunately this is not true. FPS has a significant effect on input lag. This is scientifically provable. a 60 hz monitor running at 60 FPS has a minimum theoretical input lag of 17ms, at 30 FPS this doubles to 34ms. This is a noticeable difference.
And while it's not as drastic at higher refresh rates of 144hz which many hardcore PC gamers run their games at it still has an impact. Players don't play professional CSGO at 144 just because it looks smoother.
How this translates to FH. When that PK throws out that side light your guard input takes twice as long to register on console as it does on PC. This is precisely why there are people posting that they struggle to block PK lights on Console but don't have problems on PC. It's also why the competitive for honor reddit seems to be in agreement that the game should be balanced separately between PC and Console.
I've time stamped and linked a video that goes over these concepts well (10:36 talks about input lag):
Finally I'll end with the anecdote that I own xbox, wiiu and game on PC. I have extensive experience on all of them.