When manipulating corpses, Ashema couldn't heal them as well as Skullius could, restoring function to their more sensitive aspects. He was only capable of repairing their bodies and adjusting them for exceedingly efficient physical performance by employing his perfected blood.
That said, this allowed the corpses to use his blood abilities just as well as he could, and if there was something Ashema could match Skullius in, it was his ability to use his blood in a way that was reminiscent of the Preeminent Attegoth.
Carrying his intent, managing complex tasks freely without Ashema's input…
The blood was capable of this.
…And that was why the attack that came for Skullius was perfectly placed.
The thralls Ashema had created had all met up with the birds he sent out, and they were transported to four different locations where they gathered the blood within their bodies, and with Ashema's consent, compressed it to the point where it could barely be seen.