Gatekeeping is never about adding value; it's about removing or keeping out [whatever is the opposite of value]. A subtle difference but one to keep in mind.
For example, there's absolutely positive value for users in filtering spam. This tends to be negative value for spam senders, but that doesn't detract from the user value.
Apple's version of gatekeeping is a balance between providing a user experience that they control and design, and managing/controlling competition.
It reminds me of the internet filters at large companies. Keeps out the filth and bad actors at the detriment of being on a truly free internet. That makes sense when it's the companies computers.
But not so much when you own the device.