“iCloud is not an app and does not need a delete button through the same UI” is a double-standard cop out.
Delay the deletion by 2 weeks if it’s really that dangerous, but they should still allow it.
Simply uncheck everything e.g. Photos and it will be instantly removed.
Any app could follow into your description, should they have an exception? 1Password doesn't need this? Backblaze? Amazon Photos?
I already gave a solution to the problem: Allow it, delay deletion. Apple does not need an exception to its own rule.
iCloud is an "always on" cloud storage/sync service where you choose what data you want to use it for.
These rules are for apps on the App Store.
Edit to add: There may be a reasonable debate to be had over whether there should be some visible component of iCloud that has to be downloaded from the App Store before it can be used on an iDevice—or whether the App Store rules should be, by some means, applied to the entirety of what can/does run on an iDevice. But right now, neither of those are the case, and thus, though some may find the difference between "iOS" and "application running on iOS" frustratingly slim, Apple is not, in this instance, applying its rules inconsistently.
iCloud is not an app that you can download on the App Store. It is an ancillary service for the operating system.
Great pun. :-D