"Gray has never been above Mira at any point in the series"
Bruh reading Fairy Tale... Tartaros Arc Gray slaps the shit outta Tartaros Arc Mira... And the Gray that matched END would low diff Alegria considering Alegria lasted approximately 1 attack before Mira ran out of energy. It certainly doesn't help that Devil Slayer Magic negs Demons and as we've seen with Sherria and Dimaria, Slayer Magic can dispel a Take Over form if the the opponent the Take Over is the race the Slayer is super effective against. Gray has far better versatiliy and skills, being able to attack in many different ways, meanwhile Mira is literally just "Look at me punch and create large explosions". You talk as if Mira is actually doing things... She one-shot Heine and Juliet yeah, who could give her Satan Soul trouble, which is definitely noteworthy, but that's not nearly as impressive as bullying a Full Power Invel and matching an END that one-shot Dimaria. Also while Mira did beat Jacob with Satan Soul, it is specifically noted he is weakened by having his eyes closed, it's not the same as when Gray bullied a Full Power Spriggan. That same Gray has one-shotting standard Spriggan level power that lasts multiple attacks while Mira just don't have the stamina and is weak to Devil Slayer Magic.
Stop sleeping on Gray, he isn't as strong as Natsu, Laxus, Erza and the super cracked FT Members, but he's still been above Mira since X791