Doesn't really matter, if Mira ends up being Erza tier then merely the extra energy it would take to put down Elfman and Lisanna would be enough for Mira to drain him. Elfman and Lisanna should at least be Kyria tier, more likely higher, and in this situation Laxus doesn't fight them back to back, he fights them all at once.
He was reborn after Laxus beat him. Gray kills him after Gajeel beat Torafuzar, the damage he had in that panel was from LFD Natsu not Laxus.
As for none of Gray's other stats being Laxus level, sure, but Mira's injured, so, meh.
Oooh I don't know about that partner, I'm pretty sure you've said Mira isn't affected by DeS yourself a few times, I believe "no if ands or buts" was mentioned. But I'm too lazy to find the quote lol, so you can have that for now... until we get into the real Laxus vs Mirajane argument