Future Past isn't an alternate route, it's quite literally comparable to what we have now than this terrible idea of an alternate route that's made as a sudden main part of the main game. No, it quite literally can't be a "sidequest" because the original proposition was to force a brand new route in the story that you can choose over Alear and their journey, it's not a sidequest. Age of Calamity is a spinoff and a whole new timeline unrelated to BOTW's main campaign. It's a dishonest comparison.