I think the strength of an iPad is its flexibility. You mention it's too small for watching movies, that's correct for you but for me personally (and others) it's a fantastic device for watching movies and other video. I also use it for looking at (but not editing) photos, and (with a Bluetooth keyboard) some quick terminal work.

It's also a great primary computer for users that don't need or want the overhead of a PC, ideal for people like my mother who just want to check email and browse social media.

I do agree that for many users an iPad makes no sense at all, especially if you have a variety of other computing devices that are better suited for your specific needs A jack of all trades, master of none situation.