I don't necessarily agree with writing to be a reason not to do a Arthur, but we could give a sample post to prove some form of writing ability. Plus it isn't necessarily altering Saber its just using a different character. I can understand the idea behind not changing Saber since I like the character. I will agree with the part about Noble phantasms. So yeah I can see why alt Saber wouldn't be allowed if you want to keep some consistency in universe.