And what has Gray done in this arc to put him above Erza? Before this arc, there has been nothing to show Gray>Erza, therefore, if we are assuming that Erza stagnated (which is foolish), it means at the least it still remains the same, Erza>Gray, at least until Gray shows something himself. And using the logic that Gray has a trump card, so based on that trump card, he's above Erza, is just....no words. Until he shows that trump card and it ends up being impressive, it means squat.
And as for Mira>>Erza, what's that based on? And please don't tell me because she dried up a sea or whatever facing Irene's mid-tier lackeys (forgetting that she ran out of magic a few seconds later), because that argument doesn't fly and is illogical. Erza won't be drying up seas anytime soon, because her magic is more CQC not showy, flashy explosions. Even if we are to assume Mirajane>Erza, it is still pointless, because 10 times out of 10, Mirajane will most likely run out of magic before Erza does, and she's yet to show an attack capable of one shotting Erza, which means she still loses, once she's run out of magic and Erza's still standing.