There were plenty of other problems with pre-OSX MacOS.
> The reason why people develop on Macs is because it's "close enough" to Linux to deploy with, and "good enough" as a desktop to keep tabs on most of your other apps.
The differences between x86 OSX and x86 Linux are bigger than the differences between x86 Linux and ARM Linux, in my experience. So these machines are also "close enough" to ARM servers.
> there is no development without development at home. If you work for a company as a developer, you'll be expected to maintain a machine that can consistently build and deploy your software.
Most developers have a local development environment and a separate production environment. Developers place some value on having them be similar, but they're also happy to introduce differences between local and prod for the sake of other tradeoffs.
Why can't he upgrade? (Genuine question)
People only develop on MacOS because of how similar it is to Unix, not in spite of it. Go ahead, look at how many developers were using MacOS before OSX. I'll wait. The reason why people develop on Macs is because it's "close enough" to Linux to deploy with, and "good enough" as a desktop to keep tabs on most of your other apps.
> So while there may be some premium to being able to "develop at home", clearly many developers value other considerations more highly.
Let's clear this up: there is no development without development at home. If you work for a company as a developer, you'll be expected to maintain a machine that can consistently build and deploy your software. Unless you're working as a web developer (in which case, may god have mercy on your soul), you're probably going to end up using an x86 machine. Hell, my best friend is a die-hard Apple fan, and even he has admit that he can't really upgrade his Xeon iMac unless Apple offers him an upgrade within the x86 ecosystem.