You cannot determine maturity by technological prowess.
The Edo were technologically inferior yet were mature enough to accept visitors from the sky. As were the Capellans. The existence of alien life did not appreciably impact those societies. While the presence of Picard and Troi on a world ready to make their first flight was shook to its core.
By your standards, a mature world would be excluded from the galactic mix because they have no interest in FTL technology.