It seems controversial to me because I really don't believe that creators need to create every part in order to be "doing fiction properly". If a group chooses to set their play in the universe of Frank Herbert's Dune, then there will be parts that they relinquish agency over. They do that in order to be inspired. Their fiction-making efforts, or more accurately the fiction arising as a side-effect of their play, is just as genuine and complete. I feel like this is an important point of divergence between us. If I play in Dickensian London, I relinquish agency about some things in that setting, while retaining agency about everything I care about (my character's motives, choices, acts etc). How is it that drawing on ideas like knights and orders is not surrendering agency, while drawing on say warforged would be? Is it that it is only agency if it comes out of the player's own knowledge and creativity, no matter what would be gained by furbishing them with other sources of inspiration?
A group can move away from GM authority, but for me that is moot. (At least in respect of one of your core concerns.) MOLAD was intensively focused on character journey, and that is an important reason why the game was successful for our group. I ran that game in the 80s and 90s. But the question was never whether or not authority was equal at the table, but whether interest, time and tolerance was given for players to explore character concerns within their game, other than if they can spot a pit trap before stepping on it, etc!
There is a separate line of argument that needs to be unpacked, which is that of resolution. What is different about acquiescing to Luke Crane's stipulated obstacle levels, from acquiescing to some other person's nominated obstacle level?