You do realize that Joan of Arc was charbroiled for her troubles, right
So instead of being removed from the canon, Sonia should have been charbroiled? Works for me.
Honestly, I've never seen what the big deal with Sonia is. It's not like Sonia had some awesome backstory or excellent characterization to be remembered through the ages. Plus, I've never played Legends, but from what I've seen and read, it's not even that good.
She is, from a semi-outsider's perspective, nothing more than Female the Belmont. At least Shanoa had enough personality that they could take it away and make it a plot point.
And why does IGA retconning her make him sexist? Maybe he didn't want Alucard to be great-grandpappy Belmont. Maybe he didn't like the extremely weak origin story for the VK. Maybe he thought that the original Belmont story needed to be a little more substantial than a sub-par GBA game. I see nothing wrong with that.