One key perspective I want to bring up is the impact this has to new engineers who run into differential impedance for the first time (e.g. wanting to slap on a USB connector because they're so ubiquitous). My first experience with routing diff pairs was in Altium, where you can do anything under the sun, but it was really confusing and I had to become an expert first by stitching together information from various YT tutorials and application notes.
Flux designed this with the noob and pro in mind. The pro can configure their part to their hearts content just like they can in Altium and all those impedance rules/calculations are packaged nicely for anybody to reuse. Some may call this cheating, but if I had my own design with USB working, I would be so motivated to learn those inner workings.