The more Shi Hao knew, the more unbelievable he found it. The races represented by the Seven Kings were too powerful in those days, invincible beings. Even if the descendants of later generations couldn't continue the glory of their ancestors, the torch passed from generation to generation wouldn't be inferior to Eternal Families.
Especially the founder of the stone clan, whose existence was at the Immortal King level. With such a being protecting the clan, even after several eras, it would be challenging for such a massive force to decline.
As for those eternal families in the Nine Heavens, their ancestors gained glory just because they once had a True Immortal. Logically, the Stone Clan should be more prosperous.