That's what I thought too! LOL

In their video, they're explicitly marketed as both idols and musicians.

No, both Ayu and Utada counted as idols at the beginning of their career. The only thing tying the genre, if you could even call it that, is the method through which they're marketed.

Especia is a weird choice, when the only references to be seen throughout the article were to Shibuya-kei at best with Perfume and KPP.

Perfume is still marketed as idol pop, just look at their tour website.

Passpied is pretty up your alley.