Hf shirou was dumped into the damn Kobayashi, hf didn't need to exist then. Ubw was rin's route and so if her development means hf doesn't work then so be it
The thing is, it's not fair to drop
Sakura's character development in favour of Rin's.
Sure, UBW was Rin's route, but that doesn't mean it
has to be entirely centred around Rin, or that all of Rin's development has to come in that route. Why should Sakura's character development be shunted into Rin's route and, consequentially, limited to things that are directly Rin-centric?
There is simply no way to have all of Rin's character development in Rin's route and all of Sakura's character development in Sakura's. They're just too connected. Nasu decided that it would make for a better story if you had Sakura's development in her own route and the Sakura-centric parts of Rin's development there also, because HF would just not work if Sakura's relationship with Rin came up beforehand, whereas the converse is
not true.
The only way I can see for UBW to contain all of Rin's character development would be for Sakura to not have a route, and given her nature as a character that would
massively limit her development, not to mention being unfair. You simply cannot expect the routes to be as specific as you want, because there is simply too much inter-connection.