User blog comment:IamJakuhoRaikoben/Chapter 433 & 434: Ikusatsunagi & Demolition Fist, Review./@comment-1776824-20150512000613/@comment-96.24.244.24-20150512094529

Hiro and Lucy made it clear that the celestial spirits strength depend on Lucy. When Lucy becomes stronger so does her Celestial spirits. Rather ridiculous or not it was established by a Celestial spirit mage and the creator of the Manga.

Now as far as this God the same wasn't stated. Only summoning magic that was stated to work like that is Celestial spirit magic. Not all summoning magic work the same.