Wait wait wait, okay I just read through the whole discussion about Arthur/cannon material and it would take me good deal of time to respond to all of them individually so I'll just sum up.

I don't understand why Arthur can't be male? I mean, it's the same as altering anything canon. And on that note I would have absolutely no problem altering canon so long as it doesn't change the fundamental rules/laws of the source material. It would be the same as saying the War isn't held in Fuyuki City, that seems to be an established parameter, so why not say Arthur is a male? As far as being an OC, if you change their abilities and Noble Phantasms it's as much original as anything else. I could come up with several ways to make Arthur a heroic spirit apart form the canonical form. Also, if a player's version of Arthur had an entirely different mindset and personality it's even more original. 

Not trying to be mean or anything, I just feel that it's these kinds of things that shackle player creativity.