You make a fabrial that captures a spren but makes it so the spren can still use it's powers. Then the spren makes the fabrial self aware and the fabrial is merely the way of controlling the spren. Then the fabrial is a radiant who has full access to its powers immediately because it's mostly the spren who is working through the fabrial instead of a human Radiant. Incase the fabrial in tough armor and have a quick army of radiants without training, oaths, or human squishiness.