"Arm China had stellar financial results. Arm holding, with 49% share of the company, has significant upside to gain from the market."

This is because clients and accounts that previously belonged to Arm had to be handed over to Arm China if Arm wanted to continue doing any business with Chinese firms, regardless of whether they'd actually courted their business.

This is like picking your left pocket and arguing that you stand to gain because I'm putting some of the money back into your right pocket. I'm still robbing you, even if I'm giving you some of your own money back.

Did you read the post?

This is so that they can listed on the public market.

There were no evidence that this joint venture was mandated.

And this joint venture happened after Softbank took over arm. And of course, Softbank thinks they can manage the listing process.