Well dude, biscuit is a xx hunter, with senior level experience, I think it was heavily implied in the chimera ant arc that she would most likely would have been able to take out hisoka( pre death)
phinks and feitan are senior members of the troupe, but not to the level of hisoka, ( i would go as far as to say that feitan was very near hisokas level, he wouldn’t win in a fight due to complexities of nen, but in terms of nen raw power of hatsu they were really close) again my head cannon, most people would say feitan is far below.
zazan posed 0 difficulty to feitan.
I’m gonna add an other head cannon (personal logic), seeing how feitans hatsu is a counter responsive of the damage he takes, at the level he dabbels, he would have to be serious advanced in ko, as 1hit from silva killed cheetu, that supposedly wasn’t far in power from zazan, in fact they were the same rank.
you could either take this as feitan was far above squadron leaders, or just managed to pull it off( i doubt it)
theres still a level above:hisoka,
and a level further above: biscuit.
no competition really if you seriously look at it.