Ok so I have been hearing people complain a lot about the Spriggan 12, and I think people are mixing there subjective opinion of the fights with there opinion on the power level of the 12. Particularly I hear people bash Jacob and Neinhart most, and while I agree there fights were not great by any means, I also think there just as powerful as the other Spriggan 12.
First thets look at Jacob, He has the ability to completely mask his presence, making himself invisible and making him unable to be seen,heard or smelled. He can also make his weapons such as a knife or a gun completely unseen, making it hard to discern what he is using. He is great at hand-to-hand combat, overwhelming Natsu (base) and Lucy using her Star Dress form's at the same time. He took Hits from Lucy and Natsu, neither of which seemed to affect him significantly, except of course when Natsu used his full power. Finally he has Transport, an ability that allows him to trap everyone in an area the size of the FT guild hall within a dimension where he is free to kill them at his leisure. His weaknesses are that his Stealth ability can be countered by abilities that create a large amount of light such as Regulus. His Transport ability can countered with any magic that counters Spatial magic. Finally he is honestly kind of an idiot, his strategy to make Lucy's clothes disappear and torture Natsu by making him look at her made no sense, especially because he was essentially blinding himself because he could not look at her either due to him being a "Gentleman".
Second is Neinhart, while Neinhart does not have as many Abilities as the other Spriggan 12 members he does have one very powerful magic Historia of the Dead. This magic allows him to conjure replica's of people from his enemies past, these replica's seem to have not only there original power, but also there personalities, which can physiologically damage his opponents. This ability can reach as far as the radius of Hargeon Town. Finally he can use what seem to be energy blasts that can blow a hole through a large ship. His main weakness is his durability, which honestly seems pretty bad mostly due to him being a "Summoner" type of character. I get it was Jellal who defeated him, but for any of the Spriggans to be essentially 1 shotted is a bit absurd imo. The other weakness he has is that the replica's he creates can be defeated.
So overall what i am saying is that when you look at both Jacob and Neinhart there abilities are worthy of being in the Spriggan 12. You may think there fights were bad, but I think people to often think that if they hate the fight that therefore means the Spriggan was weak. Everyone of the Spriggan 12 so far has required either a very powerful character to take them down, or a strong counter to their magic. Too me that means they have all been more or less on par with each other. However that could change if the title of the next chapter indeed means the last 6 Spriggans will be the strongest.