Same goes for Windows or Android really.

If my windows device fails, I'm not going to Microsoft. I either fix the offending part of my desktop or laptop, or reinstall the OS or move to a different OS. If something is wrong with my android phone, I'm not going to Google since I don't own a Pixel and will go to the manufacturer of the phone. If it's a purely software issue, there are steps I can actually take to flash a different ROM though admittedly it's not an easy process.

Here Apple not only owns the device but also the software it's running as well as distribution of apps for this device except for CLI tools distributed by brew or other package managers. At least with a Mac I can install and run applications over the Internet. With an iPhone that's not at all possible (not sure about the status of side loading with the EU ruling and all)

Not really the case for Android, you skip the google account setup or the amazon account setup if you are using a fire tablet and continue using the device by sideloading whatever APKs you want. Most of the times the APKs that depend on Google Play Services will continue to work fine.

I skipped the amazon account registration and directly sideloaded the Google Play apps on my fire tablet.

Even for Google TVs you can skip the setup and use the TV as is. You can sideload APKs on this as well.

AFAIK, the account setup/login circumvention is not possible on fire tv sticks/google chromecasts.

You can take a very old android device factory reset it and continue using at as an offline only device without the blessings of google or amazon. (Except FRP devices)

But that is not the case with Apple, you need to connect it atleast once to the internet to activate the device.

How many alternative operating systems work well on Apple devices?

Android phones usually have multiple options (Lineage, Calyx, eos, Graphene, depending on your particular phone) and you can always replace Windows with Linux.