But they didn’t get past signing. They did the signing steps themselves but still used a developer account. The iPhone will not run unsigned code and you can’t get a signing key without the help of Apple.
Apple has enough security to ensure nothing gets on the phone without their signing, and legally they are in full control over that and can set the terms (within what’s legal for contracts). No court or law has yet said that has to change.
People have speculated that side loading may work by Apple just letting you download the fully signed IPA file, as it would exist in the App Store. That way side loaded apps would pass the security checks but Apple is still in full control.
IANAL, but to me "allow and technically enable the installation and effective use of third-party software" sounds like a broad rule. There are a few exceptions mentioned in that provision, but it doesn't seem like a gatekeeper would be able to just come up with their own exceptions where they won't follow the rule, like "except for apps we don't like" or "except if the developer hasn't agreed to pay us".
Apple has enough security to ensure nothing gets on the phone without their signing, and legally they are in full control over that and can set the terms (within what’s legal for contracts). No court or law has yet said that has to change.
People have speculated that side loading may work by Apple just letting you download the fully signed IPA file, as it would exist in the App Store. That way side loaded apps would pass the security checks but Apple is still in full control.