I think it depends on how it is structured. Owning your own manufacturing is likely more easy to iterate than hiring other to other companies to manufacture for

I think it depends on how it is structured. Owning your own manufacturing is likely more easy to iterate than hiring other to other companies to manufacture for you. What ARM is doing is the opposite - they are the ones hired by the foundries to provide an architecture, and then it is up to the foundries to make the architecture run. This largely decouples the architecture design from manufacturing constraints giving them free reign to innovate. If a foundry can't cope, then that will not hurt the bottom line for ARM since other foundries can, whereas if you own the manufacturing, you actually have to pay to avoid obsoleteness.