Compare that to Windows, which has ostensibly less control, but I continue to find to be a massive pain to develop for.
With that said, if macOS lost UNIX, I’d be done.
There are some portability quirks for sure, though.
I tried using a company Linux device only to find that its graphics drivers weren't supported, the 4k scaling didn't work nicely without spending ~30 minutes looking up how to do it the hard way, and it didn't play nicely when connected to a normal 1080 monitor. I returned the device after (thankfully) it failed.
As OP said, it's unix, at least extremely unix-y so you don't have to learn apple specific languages. You can choose to do so for better integration to their system and vision and UI idioms (and should I say, macOS native applications are the BEST thought out applications you'll ever have the pleasure of using in user experience side). But whatever code you run in Linux will be trivially ported to macOS.
Learning a new OS is... I mean it is a new thing to learn but it isn't like you didn't learn the OS you are using at some point. Unless you think that there should be one and only one OS for the entire universe that everyone uses, this is an irrelevant point.
For the IDE, again, you don't have to, but you can choose to learn. Most popular IDEs natively work on macOS just fine, and you can just use your terminal like in any unix system, use your build scripts etc.
For macOS, you don't have to be compliant with anything, you can distribute your apps the old fashioned way. If you want to be in their dedicated store though, yeah they have rules. I think that makes sense.
For iOS, that store is the only way to distribute software and your points would make a bit more sense. But I actually am on the fence about the merit of the walled garden approach of iOS. Android ecosystem is a cesspool of malware. I can deal with malware on my computer. My computer has the resources etc. And computers are my job. But my mobile phone IMO has to run trusted code, I will happily delegate some standards to a central body as long as they manage it sufficiently well. When I install an app, I want to be sure that there are reasonable protections about what they can and can't access in my phone. I take my phone with me everywhere, it knows A LOT about me. I can't disassemble all binaries I use to make sure they aren't doing anything shady. Apple has automated tests for this stuff. I know it can't be bulletproof but it is something. They are fast to respond to exploits and they manage to keep their platform secure.
If a "free for all" device was popular, I'd still manage. I'd just have to be EXTRA EXTRA paranoid about what I install in my phone and it would decrease my productivity and quality of life quite a bit. That I can manage. But the whole ecosystem would be A LOT less secure. Not many people would exercise discipline. Viruses, malware, rootkits everywhere, billions of people carrying them in their pockets everywhere. My inclination right now is that that would be a worse deal right now for the world. While Centralisation and corporate power is something I generally despise, in this case (mobile OS, walled garden, corporate control over what apps can and can't do on their platform), I think can see the merit as long as they don't majorly screw it up.
Meanwhile, updating gnu tools is pretty straightforward with homebrew, so the consequences of this view are minimal—for me, so far.
Here is a direct quote "I actually think version 3 is a fine license" - Linus Torvalds
FSF view DRM as just being a physical version of a legal restriction, and they often quote laws that makes it illegal to bypass DRM as proof that DRM is also a legal restriction. Thus in GPLv3 they treat them as identical and they don't see it as a change in how the GPL license work. Linus strongly disagree on this.
This is very different from the Apple case and I doubt anyone can find similar quotes from them.
I think that, if GPLv3 ever gets sufficiently tested in courts all around the world (which is highly unlikely) that stance could change.
http://meta.ath0.com/2012/02/05/apples-great-gpl-purge/
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Anyway, the message is pretty obvious: Apple won’t ship anything that’s licensed under GPL v3 on OS X. Now, why is that?
There are two big changes in GPL v3. The first is that it explicitly prohibits patent lawsuits against people for actually using the GPL-licensed software you ship. The second is that it carefully prevents TiVoization, locking down hardware so that people can’t actually run the software they want.
So, which of those things are they planning for OS X, eh?
I’m also intrigued to see how far they are prepared to go with this. They already annoyed and inconvenienced a lot of people with the Samba and GCC removal. Having wooed so many developers to the Mac in the last decade, are they really prepared to throw away all that goodwill by shipping obsolete tools and making it a pain in the ass to upgrade them?
UNIX environment on Windows is just like how IBM and Unisys mainframes deal with it.
I don't care what names marketing departments come up with.
You could say that WSL is filling that need on Windows now, WSL certainly does remove some of the earlier obstacles/objections why one would want to avoid Windows and use Linux for development.
Reminds me of the days when I had to buy Windows to test if my website worked on IE.
In the case of Apple, I have to buy the hardware too!
The real Apple developer culture is around Objective-C and Swift tooling, alongside OS Frameworks, none of them related to UNIX in any form.
In case you haven't been paying attention the new network stack isn't even based on POSIX sockets.