I think the stunt double issue got better after season 2. Season 1 was pretty painful, often times it was very obvious that a double was in the shot. I think that as the seasons progressed they got a little more proficient at framing shots to minimize the number of times it was obviously a double.
To her credit, I think another big impact in later seasons was that Sarah Michelle Gellar did a lot more of the fighting sequence shots herself. It really made a big difference.
She had to put that black belt to use Lol
Sadly Eliza's SD didn't change until S7 :/
They even used her/him on Angel.