Exactly. The Elementium Plated armor wasn’t ready. When his body started to get torn to shreds the best proof of concept he had was a dragon that went insane during the process of installation. He, in his own mind, was still quite sane so he didn’t want that so he went with Adamantium plates as a stop gap to literally keep himself together.
I say that he always planned for that…Cata Deathwing look with his armor. It just wasn’t ready by the time he had to leave. Let alone when he had to keep himself from being literally being ripped apart. Now for what purpose he wanted that armor is up for debate. Could it have been originally developed to be used against the Primalists in their war? Possibly but I believe he always intended to use that armor against his fellow Aspects.