iOS is still useful without an iCloud account. Everything still works. Calendar, Calculator, Contacts, Safari, Music, etc, on and on all work just fine. You can add any number of third party services with the email app. All you loose not logging into iCloud is sync'ing of said data to other devices. It's a local only device at that point.

Pretty sure the same stands for Android.

What do you mean with third party services? Apps? You can download (free) apps w/o an Apple ID?

No. I mean you can use the included PIM/multimedia apps with any current service you use without using any Apple account. Just goto accounts and passwords under settings and add your preferred service to integrate with notes/email/contacts/etc.

Sure I would say this would make it more of a feature phone but the device itself is quite usable without an iCloud account.

The Windows Store (now called the Microsoft Store, apparently to match the name o their physical stores), does allow one yo download free programs without using a Microsoft Account. I'm guessing you might need one for paid programs, but I've literally never tried, since this is a PC, not a phone/tablet.