The Godfather knew that he would not be able to stay with Ainsley and the Sloan family for a long time, so he just wanted to leave a few more trusted people and even treasures to help the organization of his beloved disciple.
Now that Axelle had a chance to be a domain master, the Godfather didn't want him to be so reckless in trying to evolve the domain in such a short time.
If Axelle was given a chance, since he was an elf, and he would live longer than many humans, not to mention this elf was also a domain master...the elf would be able to evolve his domain sooner or later.
With his long lifespan, he could evolve his domain slowly, and in the end, he would become a strong force for the Sloan Family.
And because he could live for a long time, maybe a few hundred years, the Sloan Family could have a backing from a domain master for so many generations.