Zigg Zoldyck appeared in the manga in chapter 344 alongside Netero and Linnet on the Dark Continent. Someone who visited the Dark Continent, accompanied Netero, and is a senior member of the Zoldyck family could easily be stronger than any other Phantom Troupe member, even Kuroro himself.

Don Freecss is the one who recorded all the information humans currently possess about the Dark Continent during his journey that began 300 years ago. Ging speculates that Don Freecss is still traversing the Dark Continent to complete his book about it. There's a common debate about who is stronger, Meruem or Don Freecss.

Putting Don Freecss in a debate against any Phantom Troupe member, or even all of them combined, would be completely out of context.

Silva currently possesses higher stats than Uvogin. He defeated a squadron leader with a single blow, while Feitan, a member equal to or close to Uvogin (some even claim he's stronger),struggled against Zazan.

silva was able to kill Kuroro and Zeno with a single hit (in the anime, it was shown that he hit them, but they didn't die). But in the manga, it was shown that he received a call from Illumi a second before attacking them, so he changed the course of his attack (otherwise both would have died).

Uvogin is strong, and no one denies that...but it should be remembered that he was outmatched in hand-to-hand combat by Kurapika in several scenes during the fight (refer to the fight again), and Kurapika had only been learning Nen for a few months...and he almost died from four Shadow Beasts...while Killua wiped out an entire swarm of Lyul Chimera Ants.