Linux usability can actually be pretty good, but it's dependent on familiarity, the desktop environment, the distro, the choice of installed applications; everything is customizable, and making most of that customization requires a willingness to research, understand, tinker.
An iPad is locked down to the point of hurting usability, the 'share' system is vastly inferior to Android's 'intents', split-screen mode just recently arrived, mouse support is intentionally missing. Trying to use it as a desktop replacement is borderline masochism. Frankly, it's nothing like desktop Linux, even if you're in an unfamiliar desktop environment.