I was really hoping for ''Mael'' to be the final AA for a reason, but I guess we should be thankful for Elizabeth right? Besides Derieri, there's no top tier female fighters, and she's not really ''top tier'' anymore.
Mael will possess Tornado and Ocean, in honor of Sariel and Tarmiel.
Mael's base power is actually 190,000 (still weaker than Ryudoshel at base). When he became Estarossa, Gowther depowered him to 60K, hoping that Estarossa would surely die a pathetic death against his best buddies, the Archangels. Mael absorbing more commandments was not anticipated by Gowther.
Flash has its own God's Domain that looks like the Mirror Dimension. Here, Ryudoshel can create an unlimited number of mirror clones of himself who are as fast as him and can teleport an enemy anywhere in the dimension. However, it still the same "match user's PL to escape domain" weakness.
The Supreme Deity will be the next enemy.
The Supreme Deity needs Meliodas to break the Reincarnation Curse so that she can possess Elizabeth's body without dying and exist in the Britannian realm.
The Supreme Deity is hiding inside the Horn of Cernunnos. She couldn't break Elizabeth's curse from the Horn.
Escanor is the Sun Grace itself, inhabiting a human body that was supposed to be stillborn. Mael refuses to forcibly absorb Sun again since it has a consciousness, refusing to take another entity's life and freedom needlessly (something he knows well as a prisoner of his own body).
Sun is the only Grace that has its own consciousness, and it left Mael's body at its own discretion when Gowther fucked him up. Only Mael and the Supreme Deity knew this secret.
While Sun has no God's Domain, it is also the only Grace that has the ability to grow stronger by itself as it grows fighting experience, independent of its own wielder. All the other Grace's power is tied to its wielder.
All possessors of the Graces has their will bound to the Supreme Deity. This means that the Supreme Deity can control Mael, Ryudoshel, and Escanor against their own will... but this decreases their fighting ability, due to losing their own fighting will/intelligence (similar to Edo Tensei).
Supreme Deity has a love-hate relationship with Elizabeth because 1) Elizabeth the only Goddess that consistently refuses to submit to her and 2) Elizabeth's powers of suggestion, manipulation, and control can potentially rival hers.
The Supreme Deity grows stronger the more people she mind-controls into submission and fanaticism, and she can also tap into the powers of her worshippers.
The only creatures she cannot mindcontrol are Demons, because they either die before they even submit to her or survive without being controlled, thanks to the "Ark counteracts Darkness" logic.
After Diane's powerup her control of the earth will be so powerful that when she uses Gideon's lightning rod ability to channel enemy attacks into the earth, she'll actually be able to fully control that energy and use it to power herself, her attacks or her golems.
This is a good idea IMO. You could have it get to the point where the Dolor Dance is vastly expanding the amount of energy she can use by drawing up tons of energy from the earth everywhere that she is moving around, like a geothermal vent. I'd even have it so she could have blasts of energy erupt from the earth at will with the right movement. Basically, bypassing the energy capacity limits of her own body and increasing her effective battle power to an extreme degree, because she can use all the energy from the nearby earth. She could even use earth manipulation to make tunnels so that she could use actual legitimate geothermal vent style tactics in drawing up a lot of energy from the ground. Although since she's Diane, she'd prefer to do so somewhere where it's a wasteland or something and she won't harm creatures living in the ground. But basically, using your idea of sending attacks into the ground, with the right method she could turn that into a direct counterattack where the energy sent into the ground comes back up somewhere behind her, and ends up earthbending an attack at them. Even if she can't add it to a reservoir of energy that she has available to use, she could use it like that in something similar to the idea of judo martial arts where you use the momentum of something to your advantage without having to turn it around.
If you guys read the Dragon Ball Super manga up to the most recent parts, here is a spoiler from the latest arc relating to the idea of her using energy from the earth.
Basically, you could have her use Moro's style of drawing energy from the earth, just without the 'draining the planet dry' part. Diane could knock someone into the air with earthbending, then release geysers of energy from the earth that just incinerate them. Who knows? Maybe with Dolor Dance she can even manipulate this energy at will and redirect it to hit opponents.
When causing eruptions of energy:
Now she should still be earthbending of course, or else it would be too much like she is no longer using the earth, but I still think using the energy of the earth is a good idea for her fighting style. Maybe she learns to create a rhythm with the energy coming from the earth where she isn't even using her own magic for much of the earthbending, or she's just using a little to prompt the reaction from the earth. It could get to a point where a lot of her attacks might look effortless, or her evasion could just go with the flow of the current she already set up, simply releasing a block on it so some of the energy in the earth pushes the rock she's standing on or is near in a direction she wants. Which could also make her evasion look more effortless or more like a dance. For example an enemy shoots an attack at her, she releases some energy from the ground via dolor dance, which she absorbs causing her to move with its flow, while simultaneously the ground in a forwards curving arc in front of her is also getting affected as she does a spin clockwise, her left and right arm motions matching the diagonally rising earth shield as the ground under her feet slides clockwise in a circle allowing her to move her feet without even having to lift them off the ground while she moves her arms to make the wall. Or something like that.
Overall it seemed like there were a lot more possibilities with it and it mostly just didn't get used as much as it could've.
My headcanons are -
One Escanor is still stronger than Current King and late noon mael.
Mael would be the leader of the goddess clan and in due time he would become the most powerful goddess clan member in history.
Demon king absorbs the induras this time.
A supreme being much beyond the likes of SD and DK
A human beyond gods level of power(Not Ban)