First things first, let's NOT talk plot details out of spoilers please...

Second general thing: you're assuming that all NPs and skills are always active here, such as Abby's and Dantes. 

Okay, on Abigail: she would by necessity be weaker than in Salem because [i]Salem was a completely ridiculous case.[/i] [hider=Spoiler]She was A) still alive and everything, not a Servant, which is always a benefit (compare how absurd CasGil wound up being even whilst restricting himself because his offensive power wouldn't help), and B) had gone completely out of it and [i]wanted[/i] to destroy the world. Even whilst indulging her powers when summoned, it's limited to anti-unit because she's not a bad person. Anti-unit that cannot instantly kill Servants. That's not Gil-tier. The theoretical ability to drive everyone in the world insane if you're literally tortured into it and not stopped in time (this scenario seems to allow for similar observation and containment; the OP mentions Animusphere) is not comparable to Gil being able to, well... Avalon will let you survive. Otherwise the city would probably be destroyed at minimum before enough anti-unit NPs were used.[/hider]

Dantes: sure, he has powerful NPs. His skills are also bad. Enfer Chateau d'If obviously isn't permanent, because his Agility is merely C--it's an activated ability with the associated drawbacks and costs. Monte Cristo Mythologie is useful, but it's also only C-Ranked; what the wording [i]specifies[/i] is that the flames it creates are able to harm souls. This is useful (it's a magical attack and can harm Servants) but also not the same as "super effective against Servants". Like, that's the bare minimum to hurt them. It's all fine.

[hider=Solomon]Ignoring the fact that his mere application does kind of spoil the entirety of the first arc of Grand Order, and Solomon being horribly broken...

The guy is just plain unsuitable as a Servant because of his connection to God. It's basically bullying. And there's no way to app Roman.[/hider]