Random rant but I really want to talk about this.
I believe with my whole heart that any character that gets a redemption arc (with a couple exceptions I will get into) have their powers and abilities nerfed.
The thunder legion- All shown as strong mages. Freed was able to hold his own for a good while against Mira's Satan soul which is nothing to sneeze at, he was able to keep runes up across the entire city while doing so as well and was also selected for S-class. Evergreen was also selected for this and fought Erza for a decent amount of time, even if she also did loose. And Bickslow, despite not being selected for S-class like his teammates is powerful in his own right, after all he helped fight against 4 Grimoire heart members at once. Then during the Tartaros arc, they are taken out at the beginning of the arc (even though Laxus walks around after inhaling more band particles than them) and then they are taken out at the beginning of the Alvarez arc as well as not even taking out anyone. They took out the robot body of one of the Springan 12. That's it.
The Oracion Seiz- I don't think I need to explain how they were strong in their first arc but I've been rewatching key of the starry heavens for Au purposes and Midnight nullifies Byro's magic. The guy who could stand toe to toe with Gildarts in the same arc. Ignoring Erigor and potluck since they aren't redeemed, three of the four have two types of magic now. Cobra has his dragon slayer lacrima and has basically turned his sensitive hearing weakness into a strength by being able to send attacks from the noise around him. Midnight has his reflector magic and darkness magic giving him both a defense and a offense on top of his illusions. Racer now has his slowing magic and his speed magic and Angel has her summoning magic which were able to square up with someone on Freed and Gray's level. Then the Tartaros arc comes, and putting my rant about Midnight's appearance to one side (like seriously how did his hair go such a desaturated grey, his skin turning sickly and his eyes going from red to grey. That doesn't make sense because he looked way different in Kotsh and Alveraz) Jellal should have had his ass handed to him by the seiz. Also I'm sorry but am I the only one that finds it kinda wrong that Jellal, the guy who had them continued their enslavement for who knows how long and then sold them off to Brain, practically forces then into his guild. And Jellal wasn't being controlled, he was brain washed. He chose his actions based on something he'd been lied to about and manipulated into believing but he had fu control. And he was never that strong and he was beat by Macbeth before but somehow wins against four of them.
Juvia- I feel really bad for Juvia because she isn't basically fawning over Gray, she is a really fun character but.... Yeah. I liked the concept of Gajeel and Juvia no longer working as a team in Kotsh because it was interesting to see two people who came from the same background having drifted apart and not knowing how the other fights anymore but that didn't really happen. So many times Juvia is just used for jokes like it's been forgotten she was S-class.
Gajeel- I am aware Gajeel probably gets the nicest treatment aside from Laxus and Jellal but see, he does still get tossed around some. My problem isn't so much his power takes a nose dive, it's more he's used for jokes so much but like, a lot of them are kinda nasty. Everyone makes fun of his singing where he can hear them but like that probably hurts his self confidence. He's putting in the effort to express himself with something he enjoys and then his guildmates shoot him down. Then when he decides to go train before fighting Laxus after Natsu gets one shot, everyone calls him a coward for running from a fight he realised he couldn't win and Lily even said that he thought Gajeel was a warrior, implying he now thinks less of him. Lily also later is ready to scold Gajeel like an angry mother. But like why is Gajeel considered a coward when honestly that was a smart decision on his part. He took some nasty hits from Laxus during the fighting festival arc and he is a lot more susceptible to Laxus' hits than Natsu. (Then again, the guild had a real nasty streak between the tenrou team return and Kotsh considering there is an episode where Lucy walks into the guild to get help after turning invisible and everyone is shit talking her, including Levy. I would like to pretend that episode didn't exist because that was just horrible in so many ways) then he's just knocked from the Fairies Vs Sabers battle, knocked out of the fight in Kotsh and it's played for laughs.
Sabertooth- The sabertooth mages are also incredibly strong but they just sort of get tossed aside more than a power issue. Yeah sure Sting and Rogue show up regularly and do something and sometimes Minerva and Yukino if they're lucky but we don't really get much from the others. Now I will admit I'm a big Rufus fan just as much as I am a fan of Freed and Totomaru so naturally I am upset that there isn't much content involving him but like they don't even get a proper fight. Rufus, Orga and Dobengal all get crucified and then we see nothing of them later on. Upsetting to say the least.
In short, all the guys mentioned deserve more screentime. You can bet your boots I'm mad we haven't seen anything of Cobra, Meredy, Midnight, Richard and Racer during 100 years quest. Like I want to see what they are doing but nah. Naked Jellal. (Also was it necessary he say to Laxus' that he had been naked. I don't think he needed to know that) and extra mad both Rogue and Cobra never got a secret art because they deserve them.