You can actually choose to not install things, my average ARK size is probably close to 70-80 gigs usually. There is also a technique online to further compress the game into about 30-40 gigs due to the poor ass optimization they used, It essentially compresses files until the game needs them/optimizes the asset files they use. It was a pretty popular trick back on Guild Wars 2
(if the embed/link isn't allowed to stay feel free to remove/edit my comment or hide it until i change it. Just wanted to link a reference, nothin else)