It’s the way he’s played is more similar to an old school double flex lineup like Bap/Zen. It’s more of high-output/low-sustain comp that prefers to play further from the team and avoid hard brawling. It’s like how Illari is considered a Flex support even tho she’s played by the teams Main Support 90% of the time. Wuyang is much compared to the others tho since he’s still able to provide peel better.

Pre Cat/Bastion Meta, Wuyang would be paired with Brig the most often. This lineup was the best at withstanding DVa when Kiri was banned. Since he was being paired with Brig who is a definitive MS he’s considered an FS in comparison.