ZUN stated in an interview in Silent Sinner in Blue that most of the viewpoints were from the human characters' perspectives, because youkai way of thinking is wierd compared to humans. I forget if he stated this was the case for the games as well, but it would explain why all the games besides the phantasmagorias and fighitng games (where it would be unavoidable) have you playing human characters instead of youkai.
Imperishable Night is an exception, but mainly because it's about a human teamed up with a youkai. So even tho youkai characters are playabe there, they're teamed up with human characters.
(Youmu's half-human, which is close enough, as shown by how she represents the human half of the ghost team. ...although solo Youmu can only get up to half human bar filled

)
Rinnosuke being half-human is probably close enough, too, which I suppose leaves Oriental Sacred Place (including when it was under a different name) as the only Touhou work that takes place primarily from a youkai viewpoint. Although fairies probably view things differently than most youkai.