I actually love the idea. Too often are roleplays scattered and not coherent enough. I love themes, foils, alllllll that good stuff. I love characters representing different ideas, I love concepts that have been shown in interesting ways through characters. To me, I wouldnt mind this at all. Sure, give some leeway for people to be creative with their character, but i love the idea of characters filling out story roles and having their roles relate and deepen the story and show something. With most groups rps you just don't get that cohesion and charqcters working off each other tbh. That's why they end up boring me so much. I actively ask my 1x1 partners to create characters that are foils to mine. Or i ask, 'what sort of themes can we tackle in the roleplay? How will the characters struggle or show their theme? How can it tie in different ways?' For a gm to have this insight beforehand, while also working with the rp'er to make a fulfilling arc with their character and development, is ideal. You can do it without the pre made roles too, but people may abide more to the theme of the story with their pre made roles.
It also makes rps a little more diverse i would say.