Nienheart summoned Historias that gave Erza, Gray, Lyon, Wendy, Laxus, Juvia and Meredy a hard time. Yes Erza was able to disspell his Historia but she also fainted afterwards. He was basically giving the whole south a hard battle and basically he took on the entire south.
While it is impressive that he gave that group a fight, there is one thing you need to consider: they were all far away from him or (in Erza's case) in a 3 on one battle. Had Laxus been near him? One shot. Had Gray been near him? One (or two) shot. His durability is what makes him so weak, against anyone who's remotely near Spriggan level in terms of offense he's almost certainly going down, likely in a one-shot.
No way in the world should people like Invel/Bradman/Serena be ranked above them.
Jacob and Wahl are debatable due to their hax but Neinhart? I disagree, and I could make a case for Jacob and Ajeel being significantly inferior to them.
Serena took out the GOI but they are nowhere near the FT mages level currently. He attacked team Natsu and even as a historia failed to do any damage to them with a combination of 3 attacks.
The GOI may not be top tier (though I hold Hyberion at around Erza's level due to what he did to Goddy) but that's no reason to downplay God Serena given that he wrecked 4 of the best mages in Ishgar without using his Dragon Slaying magic. On top of that Gildarts outright said that Goddy would give him a run for his money, maybe even beat him. God Serena is definitely above the likes of Neinhart, Ajeel too due to his Water and Gale Dragon Slayer magic.
Invel froze Team Natsu but they all broke out. His chains while impressive were overpowered by Juvia's and Gray's will. He wanted them to fight and kill each other but they said no a "Killed" themselves. Then he proceeded to get destroyed by DeS Gray. Even before the chains DeS gray wounded him with an attack.
To be honest Invel insta-freezing team Natsu is a very good point; in Invel's favour. They were all trapped for a length of time, had Gray not been fighting him he could have killed them. About the chains, the specifics don't matter, at the end of the day it got someone killed (Juvia only survived due to Wendy) so the technique is still pretty good in my books. His durability is kinda standard IMO, he's weak in CQC but his Rainment makes up for it against most opponents.
Bradman took out lackys of Sabortooth. gave Gajeel a decent battle. The only problem with him is that all his curses were countered by Levy and that his anti magical particles did nothing to Levy.
Bradman no-diffed members of Sabertooth to the point where his literal appearance made them flee. His battle with Gajeel and Levy was actually a lot more impressive when you consider the following:
- Gajeel was completely immune to MBP's.
- Levy's mask stopped MBP's from entering her lungs (this is when they're lethal).
- Levy helped remove curses like Tenchi Kamei and the Second Seal (both of which would change the dynamic of the fight).
- Bradman didn't use any of his hax curses (Macro, Enhancement, Sensation etc.)
- It's hinted Bradman wasn't going all out for the most part (he says that he hasn't fought in a while and will fight to his heart's content).
- He was pretty much stomping Gajeel, Gajeel couldn't touch him whilst Bradman was mocking him towards the end of the fight.
With the above being said there's also the fact that he was hardly going for Levy, all of his attacks were aimed at Gajeel (as Onimaru showed), the only reason Levy was damaged was due to his AoE.
In addition to this (and this is the most important part tbh) Bradman has a distinct advantage against any mage without special lungs as his MBP's will kill them as they try and fight him. When we first see him he has a group of people running away bleeding to death due to the MBP's, the only reason that didn't happen in the Gajeevy fight is because:
- Gajeel's Iron Lungs
- Levy's mask (and even this was only temporary given how she collapsed the second it fell off).
Gajeel and Levy were the closest things to perfect counters of Bradman and he still slaughtered them. They were lucky that Gajeel managed to go into Dragon Force, otherwise Bradman would have killed them (Levy was basically defenseless and Gajeel was being toyed with).
So with that being said without a doubt those 3 spriggan are the weakest.
I think with the above that I've proved they're not the weakest members, Neinhart is solidly at the bottom due to his paper durability and Jacob and Ajeel are definitely not above Bradman, God Serena and Invel, though I feel we should debate that after Neinhart has been sorted out (though like I said, I see him as the worst S12 member).