Actually, whilst the settled states had the ability to produce more weapons, there is little evidence to suggest that they were any better, and the overwealming dominance of Nomad cavalry in China suggesta that Tang soldiers quality was inferior (eg tiny forces of Uighur - 4000 lancers - were decisive every time they interviened)
Both had their qualities, and its relative. Li Jing clearly mentioned it in his book of military. "When Nomadic empires are strong they defeat and pillage Chinese dynasties, when Chinese armies are strong, 10,000 men from the central plain could annihilate 100,000 nomads."
Nomadic cavalry is far from "overly dominant", warfare in central China is still INFANTRY based. 4000 Uighurs, played a desicive role, but they didn't win on their own, they charged when the battle was indesicive between Guo Zi Yi and teh rebels. It wasn't everytime, because their second battle in 758 was a defeat. Followed that, they had no desicive victories whatsoever, until their armies were finally destroyed by the Kirghiz, and the remainder hordes scattered with royal group destroyed by the Tang army.
Then we got the example of Li Jing's 3,000 men defeating 40,000
Tujue. Li Si Qi's 6,000 soldier defeating virtually the whole confederation of Xue Yang Tuo numbering over 100,000 in size.
And Su Ding Fang's multiple victories against the Western Tujue Khanate with only 10,000 men. Just about every encounter between the early Tang emperors was a defeat for the nomadic confederations which outnumbered the Tang armies. Mocho was able to pull off many victories, and the Khitans too. But the professionalization of frontier units udring the Kai Yuan turned the tide. Mocho's son was killed and the Tang also defeated the Basmils with the help of Uighurs.
"I doubt any nomads can have the same quality metalurgy of a sedentary civilization, especailly when it involves the bessemer process, which the Tang had. "
They don't need to, they can import. The age of fragmentation china is very iopen to pillage and illegal exports. Tujue probably had a great number of Chinese weapons as the Mongols acquired from the Jin.
"Uygher troops were probably of superior quality than Tang troops overall(key word, meaning NOT in weapons quality), but for nomads it depends on who. Look at DingFang, who outnumbered 10 to one can still beat off an alliance of nomads(if I remember correctly). Then there's LiSiQi, who beat off Xue Yang Tuo when outnumbered 3 to 1."
LiSiQi's numerical gap is more around 16 to 1. The Xue Yang Tuo confederation never recovered. They got destroyed in the following year, by the Tang and Uighur armies. The basic skills of nomadic armies are natural better, but their discipline and fighting ability isn't nesessarily superior, the Uighurs were defeated many times by both the Tang and Tubo. Their superiority lies in their vast ground of operation, the steppe of Mongolia, yet when Tang was at its height, they could do little but follow the rules of Tang politics.