Apple writes these rules, and as platform owner of iOS they can design the rules not to apply to themselves. I don’t think that’s a good defense against the obvious hypocrisy here. A major part of Apple’s playbook these days is to design some policy that has the effect of advantaging themselves vs. competitors, while also helping the consumer. I think it’s an effective strategy, but it also deserves some criticism. The consumer would be helped more if Apple treated their own services equally.
Arguably, yes, for some people, iCloud is more important than, or as important as, their bank account if their iCloud is used for disaster recovery of their primary computing device data, including passwords. Maybe even the password for their bank account.
How is this a meaningful distinction whatsoever? There are countless apps that allow you to sign up for an "always on" service. Should they be exempt from allowing you to delete your account as well? Or is that privilege reserved for built in bloatware?
iCloud is part of the operating system, and, most importantly, it is not downloaded through the App Store.
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.
Are you being deliberately obtuse or just really not able to understand that Apple provides two things: 1) an operating system with ancillary features and 2) an App Store with applications for sale?
iCloud is not an app that you can download on the App Store. It is an ancillary service for the operating system.