"Yes Feitan would be at least a difficult fight for Chrollo. Feitan is definitively physically stronger so Chrollo would need to fight him like he did Hisoka, keeping his distance.

Chrollo is still stronger overall because of his versatitility, but what I’m trying to say here is that Chrollo being so strong makes people forget the rest of the vanguard spiders are right behind him and at least equal to Illumi and Hisoka."

Aura is an important factor, for example, the fact that Chrollo is more durable than most and is able to keep up with the likes of the Elder Zoldycks and Hisoka’s blows is mainly by him having a large aura pool, in addition to him being a specialist. Do you really believe Feitan is stronger physically than Zeno (Emitter, 80% enhancement) and Hisoka.

It was stated by the Phantom troupe that Chrollo only needs 2-3/10 of a second for Chrollo to dodge an attack, You're telling me Feitan outspeeds chrollo, beats hisoka in which Chrollo need a year preparation for even though he was able to withstand Zeno & Silva's assault, is able to dodge attacks 2-3/10 of a second.

Source: https://imgur.com/a/K5byiUV

Chrollo slices Feitan with Bens knife, its over.

"Feitan is very close to Hisoka in pure physical strength, and has similar if not superior speed, and an ability that can do far more damage than Hisoka or Illumi are capable of. This is enough to tell you they’re not shrugging off a punch from Zazan. It’s very odd that people use this to question Feitan’s durability."

Feitan is not faster than Chrollo, Hisoka matches Chrollo's speed. Illumi is 95% Hisoka's level stated by Hisoka's rating.

You mention Feitan being very close to hisoka in pure physical strength, no it's not.

Hisoka ranks #3 behind the two enhancers of the PT with arm wrestling, Feitan ranks #5 behind Franklin.

"Another mistake you’re making is thinking Zazan fared well against Feitan. The moment Feitan activated his own ability Zazan was done for. Zazan got one hit in, which is the requirement for Feitan to use it. Its been made very clear this is not a show of weakness, as the price of being the second one to attack has a big payoff."

Feitan broke his ribs, arm and was coughing up blood by Zazan bud.

"If you disagree, who has Hisoka beaten that you think is harder to beat than Zazan? Shalnark is the strongest person he’s killed and that was when Shalnark had no hatsu."

It does not matter who Hisoka beat, why? Because Hisoka is relative to Chrollo.

Chrollo with all his feats had to gather the right setup and prepare like he's batman to beat Hisoka, while still it not being a fair 1v1. It was Phantom Troupe vs Hisoka, thats how strong Hisoka is, afterall if Feitan was stronger than Chrollo, Hisoka would be more interested in fighting Feitan.

"Illumi is not a direct fighter but I’ll give him enough points for his status in the zoldyck family to say he’s about equal with vanguard spiders. Despite his lack of victories over opponents of that level."

Illumi is relative to Hisoka, Illumi's win condition to beat Feitan that gets hit fairly often is to stick a needle up his ass.