With a barrier breaking ability bestowed upon Ramiel, he easily damaged the Hexadrom to the point that it no longer could sustain the barrier on the clouds. The Hexadrom utilized almost all of its mana to repair itself and can no longer support the barrier projection.
The Hexaminis are the same as they were not created to easily deal with Principality level angels. Back then, most angels above the third hierarchy got sealed in the Silver City as punishment. Some of the strongest were not sealed but that did not mean they cannot escape being depowered.
The angels' power mainly come from their connection to the Silver City as it was a city always being bathed with light. It is also the only way for angels to stabilize their bodies that are almost purely spiritual lifeforms because they are made from bodies of fallen gods. Gods are also spiritual lifeforms which is why they cannot easily penetrate the barrier between worlds.
