I think you're missing the largest part of that, though, and that's what makes your statement incorrect. Apple is not blocking anything that Epic can do with the Unreal Engine. What they're threatening is to revoke the assistance that Apple has always provided Epic as a partner. When WWDC and other presentations roll around, Apple always has presentations from Epic on new games that are coming out. That partnership has, in the past, included early access to dev tools and frameworks (like Metal and ARKit), direct access to engineers at Apple who help Epic optimize their software for Apple hardware, and also a direct feedback channel for licensed developers using the tools that Apple and Epic developed together. Apple is saying that, by violating the terms and losing their developer license, Epic would also be losing this partner access. After all, how can you partner with someone that's actively working against you?
So, to be clear, development for the Unreal Engine would absolutely be impacted but that is not the same thing as "blocking Unreal Engine". Apple can't block the Unreal Engine as a whole since developers license that separately from Epic.
I think this is the more pertinent bit of that email:
> You will also lose access to the following programs, technologies, and capabilities:
> All Apple software, SDKs, APIs, and developer tools
If Apple had carried out that threat (which this injunction prevents), it seems like Unreal's development would have come to a halt, as Epic employees would no longer be able to legally use XCode etc. I suppose they could have kept writing code in a text editor, but there would have been no practical way to test it.
So, to be clear, development for the Unreal Engine would absolutely be impacted but that is not the same thing as "blocking Unreal Engine". Apple can't block the Unreal Engine as a whole since developers license that separately from Epic.