It is not double work, you are only assigning related products for that respective product, what you say is "missing" is some additional functionality to cross-link related products.
But with a proper multitool module like QuickUpdate for Prestashop, you can do what you mentioned and even more actually - assign related products to how many products you want at once, including the cross-linking!
If you access the live demo, the tab for "Related Products" functionality is named "Accessories" because this was the name of the functionality initially - same function different naming. (https://prestashop.endpulse.com/prestashop-addons/13-presta-quickupdate.html)