First time poster here, though a long time HXH fan.
First of all the talk between Zeno and Kuroro just goes to reinforce the fact that you cannot know anything for sure unless you know each other's ability completely. It's pretty clear Zeno is far stronger than Kuroro in any tangible measurement, i.e. aura level, raw power, experience, and probably even tactics (Zeno saw through all of Kuroro's tactics easily). However this doesn't mean much when you don't know what kind of aura power the other guy may have. Zeno is an assassin who is very interested in getting out of his mission alive. He is not going to say he has this much aura power so no way he's going to lose. He clearly has no idea what kind of ability Kuroro may have on that book, so even though he can tell he is stronger, he's not going to risk his life for no reason. That's why he said he'd almost certain win a normal battle but can't say the same if it was to the death. For all he knows maybe Kuroro has an ability that only works on assassins!
Meryem cannot be compared to the Spiders, even in his initial form. Novu said that it's okay if the rest of the assault team got wiped out by the Royals as long as they defeated Meryem. This implies by himself Meryem is considered a threat to humanity itself. If the Spiders can defeat him that'd mean they too are a threat to humanity itself. This simply is not true. If Kuroro didn't hire his own assassins there was a good chance a significant portion of the Spiders would be taken out by Silva and Zeno.
At any rate a fight between Meryem and Spiders would have answer the question how is the fight going to start. If Meryem is in 'dinner' mode, the fight would begin with a significant portion of the Spiders missing their head or at least a limb, possibly including Kuroro (there is no reason to believe he is the top 3 most capable physical fighter out of Spiders themselves), and of course each person he kills would make him even stronger. When Meryem first met Zeno and Netero, Zeno and Netero were momentarily distracted and both of them realized that they could've died for just taking their eyes off Meryem for even a split second. If being distracted for a split second could've killed Netero, I don't see how the much weaker average Spider member would stand a chance even if they've their full attention on Meryem.
However, Meryem could be in his more human side, and in this form he clearly wants to find a challenge. After all, he gave Netero a considerable handicap (he promised he wouldn't kill him). I'd imagine Meryem might give Spiders something like no killing (from him), and he must give the Spiders some kind of lead time to charge up attacks. This criteria is crucial because if Meryem can attack first he'd just remove the limbs of all the spider and that'd pretty much stop any of the abilities the Spiders possess. That said even if they have time to plan and execute an attack, there's no way the Spiders can dish out enough damage to hurt Meryem physically. I'm going to assume there's no way they're going to be able to stick an antenna in his body (the antenna wouldn't stick even on grunts without an opening), and Phinx won't just get to spend his arm a million times. The only attack that may affect him is by sucking up his blood (Shizuku). It's pretty clear that he does bleed and presumably even he will die if he lost all his bloodm though given Shizuku's rock bottom physical ability, it's hard to imagine how she can continue doing that once Meryem realize what's going on.
