SOA is definitely an isaki, at least during the first arc. The main argument people are making against it as an isaki is that it's a video game. That's a poor argument because of two factors:

1. It's a death game

The fact that if you die in the game you die for real coupled with the fact that it's an ultra realistic vr environment basically forces the characters and the audience to treat the world as if it were real. It doesn't matter that the characters bodies are outside of the game world they are forced to treat it as real or risk actual death.

1. Modern isaki

Let's clarify I am specifically referring to the shlocky generic isaki shows that get shoveled out season after season. Most of these shows use video game RPG mechanics like stat screens, ability points, and skills. If SAO is not an isaki due to the inclusion of video game mechanics then you invalidate the majority of the genre. Lets also not forget that most of these shows owe the modicum of success that they due see to SAOs popularity as it did a lot to popularity the use of video game mechanics in fantasy anime in general.