Well, let's see Erza's proper fights from OS arc
Midnight - This was one of her best fights. She won here with strategy and not any adrenaline.
Erza Knightwalker- Again a good fight, where they rivalled each other and not much PoF.
Azuma - All the cancer starts from the last part of this fight. Azuma for some reason, took the powers of all in FT other than Erza. Here, she won with power of friendship and love. Erza in normal combat was matching Azuma and when he took the powers of FT and got advantage, she used a final adrenaline push with all her will power to get the advantage and tenrou tree supported her and at that moment, she was temporarily the strongest. This wasnt any permanent powerup.
Kagura & Minerva - Pre SO Erza matched Kagura evenly and with a slight adrenaline push won against her. Mashima made it over the top by crushing her foot. To face Minerva, she didnt have MP and she released her Second origin, which helped her to don the nakagami armour which was the exact counter to Minerva. Other than that asspull armour , I dont see anything wrong with that fight.
Minerva & Kyouka - Minerva was never a match to her even in demon form. Kyouka's fight was worse coupled with Happy's explanation "She's Erza." But Mashima admitted she didnt get strong to win but used her seventh sense something like in Saint Seiya I think to win the fight despite her senses being taken away.
Ajeel - Nothing wrong with this fight. Good strategy and balance.
Irene - This was one of my most hated fights in the manga. But I believe she had Wendy's help and here for no reason, her adrenaline surpassed all logic to cut a meteor into 2 and one slash a dragon which she conveniently got by Wendy enchanting her sword. She didn't get any permanent powerups for this fight other than the DS sword.
Now, lets see the Sequel
Kyria - She was affected by the hax. But later she got her payback.
Laxus - She learned enchantments and matched him because of multiple powerups she had after her fight with Irene.
Yoko - She lost R1 and won R2 with the help of team.
Suzaku - Though with surprise, she got 1 shot. Never got a rematch here.
Misaki - She used a new enchantment to win this. And conveniently her magic use telekinesis to match Misaki hax.
Signario Sisters - Trio were new to Alchemy. Once Erza had it figured out, she straight up destroyed Luso's world , blitzed and one shot her. Enny was matching her first. Then she got the nakama adrenaline which gave her the push to win. I don't see any powerups there, other than Mashima nerfing sisters by making them forgetting to use their hax on Erza and to win.
