It wouldnt make sense for Rito or League because like the cool guy you quoted said, for valve and square its a symbiotic relationship. Steam has its own ecosystem that makes it beneficial for companies to cross advertise(see:tf2 characters in sonic all stars, pipboy items for tf2). League is its own closed thing, its not a matter of riot(laughably) building lore in the long run and having it pay off(the lore in league is a running joke at this point.), but that it wouldnt be beneficial to them to do collabs. For Valve its cross advertisement- oh maybe that hardcore dota player will buy/preorder an ff game for the chocobo, and its a 2 way benefit because not only does Valve get a 30% cut from that preorder sale, but it also advertises the game that has that bonus(protard:wow where did you get that courier! Preorder? I know I will!).
For league there is no inherent benefit for Riot in having collb. For valve they get a cut for a game sold in their ecosystem, so enticing people to prekrder on their platform with a courier skin or tf2 hat does have a benefit.