If you’re talking about Zheng He and his fleet, those boats were not rickety. It was an impressive fleet. That said, that doesn’t magically give their claims in the South China Sea any more credence than arguing the British still have a rightful claim over Ireland.

Far from not a peep, China mention their "unequal treaties" and the "century if humiliation" a lot, it's a rallying cry and something they would definitely use to bolster the case they're making here. What did you mean by this?

while not a peep has come out of them about the shaming they suffered during Opium wars when western nations effectively carved up China to spheres of influence

This is the underlying reason why they don't like or trust the west. It's pretty much their whole MO and why they think Japan and South Korea will rally with them.