Unlocking Behemoth is a reward unto itself. ^_^
You collect instincts instead of gear, and unlock new creatures and skins to try out.
You get RoE shards along the way as well.
And if you do Beliigerency, you get lots of crystals and seals. (and some odes/ites)
I wouldn't say it's completely without reward. Granted, there's a lot of unfulfilled promises and potential with the content.