So far , I consider two feats in the series as outliers : Defeating Acnologia and Erza slashing Deus Sema. Because Erza's feats in that arc and now don't match up with that feat at all via scaling as well as on panel. Dragon Irene = August who low diffed Gildarts. Dragon Irene should've required at least 3 powerful mages say Gildarts , Laxus and Erza to be defeated. To add it , Dragon Irene shattered Erza's bones with a claw. If she stomped on her , it would've been over. Doesn't make sense a broken bones Erza managed to shatter a master enchant.
Neither of them are outliers.
Eileen was featless until she fought Erza. Hype in FT = shit, and unless there are no feats at all. Feats >> hype. IMO Hype should be taken into consideration, only in absence of feats.
Eileen is likely August tier in magic power, but her stats aren't all that to be admired at. Her stats were shown in Erza's fight, that does it for her. It's kinda understandable, her magic isn't typical of a front line mage or direct battle mage, but it's OP behind the front lines, as shown by her enchanting fodder soldiers to relatively strong level.
They defeated Acnologia's soul. Nothing says that Acnologia's soul is in the same tier as the real Acnologia.
Even Hiro realized that defeating the real Acnologia, with his feats, is impossible except for high tier Dragons ganging upon him. Which is why he made our Dragon Slayers defeat the soul instead.
One of the true outlier is Ajeel losing to Elfman. Elfman is pure physical attack, which Ajeel is immunne to. Even with Elfman being immune to sand in his take-over, the fight should've either resulted in a stalemate or Ajeel eventually winning (because the fight will last until magic power is depleted, Ajeel has higher magic power).
The other one is God Zeref being destroyed by Natsu. Even with all guild member's magic power, Natsu shouldn't be able to put down Zeref for a significant amount of time. Because he has infinite magic power, and this magic power should've instantly regenerated any damage that Zeref took. As far as I understand, the way Zeref's immortality works is that it prevents death and heals him whenever he has magic power. Base Zeref can be put down for good, for a while, by this logic; but not God Zeref. God Zeref should work in a similar way as Hades with Grimoire Heart worked. When Hades activated Grimoire Heart, we instantly saw him getting healed and his magic power jumping up several tiers. The same should've been applicable to God Zeref.