There are many facets to this. First of all, the App Store performs a range of services. Payment processing, the app review, hosting. For the user it is a trusted platform, where credit card numbers are not transmitted to arbitrary locations on the web, the app review and the ability to withdraw malicious applications do offer quite some protection.
From this side, the App Store fee can be justified. Whether it is reasonable or to high depends on many parameters. A fair solution would be to have the fee start at 30% and decline with sales numbers, as the review process doesn't increase. Of course, large commercial entities, who do have their own servers/payment processors and don't need a trusted site to host their apps are less happy with the policies.
But beyond the discussion about the fee, there is the aspect that Apple prevents all software installations from outside the app store. This is something which has to change as Apple isn't only protecting against malware, but also limits a lot of benign applications from being available on iOS. The first thing coming to my mind is Termux, which would instantly make an iPad much more usable. And extending that, a whole range of development tools could run way better on the iPad than it is allowed on the App Store. Just imagine a Linux VM running on the iPad...
Apple should (or should be forced by regulators) to offer a Gatekeeper-like solution on the iPad/iPhone which gives the users a reasonable amount of control about their devices.
And there is of course the content question. Apple tries to enforce their idea of "morale" onto the users. This is fine for their storefront, so to say, but there should be a section in the App Store for adult content. Especially the safe payment process would make this a very attractive service. If Apple wants to keep the "service" story alive for the App Store, they should craft their services according to the user demands, not to their ideas of what users should consume and install.