It's unfortunately not that simple. It was only considered very strong because Parallel Universe is in the same element. This gave Aether 12 Dragons in a deck, 6 of them being heavily discounted and due to >5 HP not vulnerable to most CC. If you nerf the stats too much, it becomes useless on its own, and if you don't then it's still slightly OP with PU. The last option would be to reduce both cost and stats, but that made no thematical sense at all and did very little for Aether thematically and power-wise.
By making it immaterial, zanz preserved the Dragon theme of the largest hitter of the element and it gave Aether a unique kind of offense that could actually stallbreak (Immortal couldn't due to way too low total offense). The problem lies rather with the low power of Immortal now and then. In unrestricted, that problem was abated by SoW, but not completely solved. In restricted, Immortal is sadly mostly useless.