The whole point of the mafia was that they're just a bunch of guys with machine guns without the training or the right equipment so of course they get destroyed fighting a group of aura users. While in NGL, Kite was saying amateurs can't defeat Ants even with military grade weapons (since NGL didn't really have a professional army). What exactly is so special about Ikalgo's sniper rifle compared to a normal sniper other than that his ammo is reinforced by aura? And yet aura doens't really come close to what speciaized equipment can do. The lobster guy can blow up another Ant's body quite easily (when he suspected Ikalgo was a spy) but his aura blasts has no effect on reinforced steel. Now of course since the existence of aura itself is secret in itself of course you're not going to commonly have these special equipment around, but it'd be absurd if the armies of the world don't have weapons that can deal with human beings who don't even come close to the durability or destruction power of modern vehicles.
The Spiders are much more durable than modern vehicles (Uvo can take an anti-tank rocket), and some of them have the destruction power of modern vehicles, if not more : Uvo with his Big Bang Impact, Franklin with his Machine Gun, Feitan with his Pain Packer, Phinx with his Hatsu (it must be as strong or nearly as strong as Uvo's Big Bang Impact, since his ability has a condition), Bolonelov with his giant boudler...Since there's no way a single bullet can be more powerful than
an anti-tank rocket no matter how reinforced it is, then there's no way a single bullet can do anything against the Spiders. Of course, the Spiders cannot hope to fight against an entire army (and they are not stupid enough to try) but said army would have to use something much more powerful than mere bullets. Even assuming a Spider can be hurt by a bullet, then all they have to do is to get out of the line of sight of the shooter before he pulls the trigger, a feat they are more than fast enough to pull off, even if there are more than one shooter.
For the Spiders, people grossly overrate their power. It's not clear if the entire Spiders put together can even do anything meaningful against a single Royal Guard. They wouldn't necessarily even be able to stall for any meaningful time against an opponent of such calibur, and yet Gon and Killua is expected to stall Pitou by themselves. Killua's lightning speed alone is crazily overpowered because you can't hit him and you can't avoid his hits. He can hurt someone like Pufu who has regeneration by frying his skin (and Pufu can withstand the heat wave from a Rose fine) and you expect human flesh to withstand that? The participants of the Chimaera Ants are way out of the Spider's league, even on the human side. The Spiders fought against the grunt Ants 1on1 with the exception of Feitan and it took them some effort to do it, while Killua fought an entire squad at the same time and he was already tired from previous fights, and he fought several guys who had very respectable abilities (Ikalgo and the fish siblings) by himself.
The Spiders used 6 guys to defeat an Ant squad. Several members were hurt, even ones who are specialized in combat. An Ant squad in the battle at the palace isn't even a unit of measure worth discussing. The Royals consider the squad level Ants to be of no use. Morel was fighting Pitou's remote controlled army and squad leaders at the same time and winning relatively comfortably. In the actual assault on the palace we see Killua took out two grunts in one frame, while the same grunts managed to drag on for a while against the Spiders.
What makes you believe the Spiders are so weak ? If you review the fights between them and the Ants :
-Phinx completely destroyed his opponent without any kind of trouble.
-Ditto for Bonolenov.
-Ditto for Karuto.
-Sharnalk was caught by this giant Beetle only because he let his guard down. Nevertheless, he still had a backup plan, and once he used it, he one-shot his two opponents.
-Shizuku had some trouble (and she wasn't in such a bad situation, actually), but she's one of the weakest (if not the weakest) member of the Ryodan. Yet she managed to win without any kind of injury.
-Feitan had trouble because his opponent was genuinely strong, and he still had the upper hand during most of the fight without even fighting seriously, until the moment he got cocky and was blasted away by Zazan's Emission attack. The moment he really got serious, Zazan was completely annihilated.
And they were not fighting "grunts", as you say. They were fighting Officers and a Squadron Leader, who are dangerous foes (Rammot, an Officer, managed to hold his own against two powerful Nen users
before learning Nen, and managed to survive not one, but two powerful Nen attacks).
I think you are grossly underestimating the Spiders. Of course the entire Spider put together could stall a single Royal Guards, they could even stall the three of them really. And when you say "the participants of the Chimaera Ants are way out of the Spider's league, even on the human side", that's just not true. Netero is the only one much stronger than the Spiders. We know for sure Silva and Zeno are as strong as Chrollo, and Morel and Knov are certainly as strong if not stronger than the strongest Spiders (such as Uvogin, Phinx and Feitan). I'm not sure about Knuckle and Shoot, but they can't possibly be stronger than Feitan, Uvogin or Phinx. And Gon and Killua stronger than the Spiders ? No way. They could probably hold their own much better than before, but they would still be defeated at the end.
