Page 26, paragraph 3 seems to make exactly the claim GP made. But you're correct, I haven't read all of the 28 pages of Apple's argument here. From what I have read, they don't seem to be discussing potential benefits that come from sideloading, only costs.
> Even users who decide they don’t want to sideload, and prefer to download apps
only from the App Store, would end up being harmed. They could be forced to
sideload an app they need for work, for school, or for social inclusion if it is not made
available on the App Store. Furthermore, cybercriminals and hackers may trick users
into unknowingly sideloading an app by mimicking the appearance of the App Store,
or by touting free or expanded access to services or exclusive features.
