They do, actually. The DMA is one of the most comprehensive and impressive pieces of technology focused legislation in a lifetime. It expressly forbids gatekeepers like Apple from making the process of installing applications any more difficult than it is for Apple's App Store. The purpose of the legislation is to foster fair competition. It's not fair competition if Apple is allowed to make the process prohibitively complex or cumbersome.

I generally agree, but one problem is that many of Apple's rules are enforced primarily or exclusively through policy, not actual technical permissions. This is especially true for all the high-level ones around tracking.

Obviously, things like phone book access can be solved for sideloaded apps just as well as for App Store ones – just like Android has been doing for many years.