Well, I want to mention more things about this.
In first we can emphasize that Arata in his Sword Magus form, was able to fight with a trained Akio and even defeat it.
Here we will have to take as a base other characters.
That same Akio, later could fight and "defeat" Melacoda (actually he surrendered), leader of the Malebranche.
I will not say that Melacoda is the strongest of the Malebranches for being the leader, since Rubine herself is the most powerful. However, it should be comparable to the other Malebranche, specifically Miglione, which mentions that in the past it ended up with several human countries.
So the Arata defeat that Akio, could at least destroy a country, right?
Well, if it does not work, then it can be said that Arata could fight evenly (for a short time), with Rubine, leaving both of them weakened, in addition to supporting Rubine's attacks.
It has been made clear that Rubine is the strongest of the Malebranches. Thus.
Rubine = Arata> Miglione.
Obviously, Arata was even with Rubine only through a powerup.
In things like speed of the characters, then there is the feat of Akio and Levi to dodge shots an arsenal of weapons. And although I do not know if it can be counted, Arata reacted to an arrow thrown by the same Levi xd.
There are some hax's that can be added to Arata as Reality Warping, this being able to recreate a complete city through its grimoire, also recreating people. And some that should be removed as the Time Stop, since Arata does not stop time, but can manipulate it to slow down. And his Regenerationn is not capable of enduring a magic with existential erasure, what Arata did was to use antimagia to cancel the magic of existential erasure (this in his battle against Abyss).
I hope it can be of help xd.