Your are mixing up diversity by culture and diversity through religion.
Whereby the latter was well relaxed e.g. Muslim Turks adapting and immersing in the past 50 years to Western-culture and Christians relaxing towards Muslims. A sudden spike of desert Muslims in the past 10 years has brought a lot of unrest.
As for Diversity - those Hispanics and European Americans carry the same diversity with them as Europeans. What we don't have is 52 million Bantus in Europe. So we need to rely onto English speaking music bands and didn't get a Chuck Berry or Jimmy Hendrix style of music into our European culture - also no golden sprint medals.
If you look into China's past 2500 years of well recorded history - their diversity is even higher then that of Europe and the USA.
Noodles weren't brought in or developed by Han Chinese but came in from the Silk road and Turkmen folks into China. Then refined and partially replaced by rice-noodles instead of wheat based noodles - Kung Fu Panda loves the wheat based ones.

And tea was brought in from the southern Kingdoms and Sichuan/Yunnan based cultures into Han-China.