Katrina's blessing artifact indeed amplified the power of the ice crystal Heroic Spirit, there was no doubt about that. Any Heroic Spirit or Evil Spirit he had in his hand, placed in a normal battlefield, would fully exhibit their power, and even the ashes silhouette could make use of the blessing artifact...
Although the ashes silhouette would be quite resistant to it, it was a subordinate of Zheng Yichen, and it had to follow Zheng Yichen's orders, even if its power would put additional strain on the blessing artifact. The advantage was that it could be used on his own people, which was akin to giving his own people a version of the Vampirism Skill tainted with the spirit of Evil Spirit.
It put his own people into an exalted state of bloodthirsty rampage, ensuring they don't completely lose their sanity while enabling them to fight by ignoring fear and other factors due to the power of anger...
The artifacts crafted by the two witches still had great potential for development.
