Additions for the Companion system

This is one of the few things that has been bothering me, is the fact that the companion system is being underutilized what with the Chocobo being the only companion thus far. So I wonder: what or who do you think should be used with the companion system here's mine.
Ark (hear me out)
Item to Summon: Lapis Lazuli (I know you need plumes to summon him in 9 but I have no idea as to who or where we would get plumes from)
Companion mode: After the cast time there will be a quick version of Arks summoning animation where he follows and fights as his Mech Mode
Mount Mode: This would see Ark turn into is Ship Mode where the player will then jump to board him and then fly.
While Ark (being Ark) doesn't have much in the way of Customization I'm sure he will be viable. Now it's your turn, who do you think would work with the Companion system?

Allowing mounts to fight along side you would be great. Manacutter could very well be the Ark of FFXIV, transforming upon summoning for battle.

At the current moment mounts are just a thing that people mindlessly collect, allowing them to be levelable companions would give them purpose and personality.

There's already battle animations for quite a number of mounts including the Coeurl, Wyvern, Twintania, Behemoth, and more. Utilizing these animations that already exist would be a good feature for suffering through fates and such solo.

Indeed, I also made an error in my original post, it's Pumice not Plumes that you needed to Summon Ark in 9. with that out of the way. I can (kind-of) see the Manacutter either being converted or a new model based off of Ark, Granted I don't know if any of the Iron works crew saw Ark during the fight, so It may end up being a mogstation Companion(seeing as I have no idea how that would be integrated into the story at all). At any rate I would Agree that making mounts Companions would be awesome, And I would love to spitball ideas to make this a plausible Idea.