Decimate... Has worn out its welcome for me. It doesn't feel as nice as Steel Cyclone, especially with the long delay on its damage >.>
So yeah...
Personally, I'd like it if Overpower became PBAoE instead of Cone. (So that you don't have this awkwardness wherein Overpower is a Cone and literally your other 2 AoE's are PBAoE...)
With Mythril Tempest being 2 really wide swings (Like, starting and ending with the axe head behind you) that sends out an elongated x shaped gash in a PBAoE.
Steel Cyclone upgrades into a new AoE that continues the "Cyclone" theme... Like, Fell Cyclone or something. With the currently shown Chaotic Cyclone animation.
Chaotic Cyclone becomes more fancy with fiery particles, have the ground crack like with Decimate maybe also with a landing that includes slamming down your axe causing an explosion with appearance similar to the orange/black sphere from Infuriate's animation.
Inner Chaos should be something similar to
Disgaea's Colossal Fissure. Where you do an upwards swing with your axe head being all fiery and leaving a fiery trail (Similar to how DRK's combo skills leave that shadowy trail) and hitting the target causes a small fissure under them, then you use the momentum of the swing to jump up and then come slamming down your axe onto the face of your enemy, causing the fissure to also errupt (Similar to Upheaval).
Also, I think it would be cool if Fell Cleave itself also had an update to its animation. Like, it would be super neat if it would like each usage alternate between a / or a \ slash where after the powerful chop you make, it then does the spinny-death-blades animation as it cuts deep into the enemy. Would also make Inner Release look way cooler, when instead of just giving a little love tap with each "Cleave" you're there swinging wildly left to right with powerful feeling attacks.