As seen with Kormir, beings CAN ascend to Gods, given the right circumstances/opportunity. So, I believe Abbadon was indeed a Mursaat at some point in his life before maybe "ascending."
At this point, the mursaat realized that any of their race could become a god, and they stopped worshipping the old gods, and elevated themselves to the position of the "unseen gods" of tyria.
In response, Abbadon tried to assert himself over his former fellow mursaat by waging a war to make them realize his godliness so that they would worship him. To serve Abbadon's war, the titans and jade armors were animated to fight against them.
At this time, like long before, the Seers were at war with the mursaat (reasons unknown). The Seers saw that the mursaat were fighting battles on two fronts, and attacked in one last "surge" hoping to finally gain the upper hand in the war. Unfortunately, their plan backfired and instead nearly all the Seers were killed in this.
Abbadon was loosing his war, because the mursaat discovered that they could "seal" away the titans, and destroy the jade armor and put the soul of a fallen comrade in its place, making it allied to the mursaat. Abbadon soon abandoned his conquest and instead turned to Jadoth and the easily swayed humans to serve him.
He finally used these humans to build yet another army even more vast than the first. Although the mursaat were not allied with any god, they were allied against Abbadon, and because of this, they were aided in this war by the forgotten.
However, the mursaat spellcasters were all busy sealing away the titans, so instead the less appreciated warriors and rangers of the mursaat were sent to fight alongside the forgotten. The margonites were defeated, creating the Crystal Desert. However, because all of the mursaat warriors and rangers went leeerroooy jenkins while the forgotten stayed back, almost all died. During this time, the mursaat's separation became "classism" among themselves, and those that returned alive were slain at the hands of their own brethren.
However, because the forgotten were declining in numbers, they found it usefull to animate the armors of these long dead soldiers to serve as asistence in their guardianship.
So basically, the mursaat knew that they could ascend to gods long before we did, and classified themselves as above us because of it, and thought it was specific to mursaat spellcasters possibly.
Another thought that kind of messes up all of this, unless I could come up with some general time line for all of this, is that the enchanted armors were the "old" mursaat before the race itself evolved into its pure form of just spellcasters.