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In order for it to pan out the way you're thinking, they would have had the artists make the Miku designs first, then the music producers make the songs around those designs (which restricts their creativity and shoehorns them into working off someone else's creative design process) and then finally have the animators build off that.
I'm guessing the end result would have been more disappointing from a quality perspective even if it would have been more cohesive.
At first I disliked that the song had nothing to do with the designs or typing, but then we couldn't have had a clever Miku song that overlaps her failed attempts at capturing your heart with the PoV of you being a Pokemon she literally captures with a heart ball. It's cheeky, it's cute, and I appreciated it more knowing that Deco*27 got to be fully creative with making a Pokemon themed Miku song. Like I felt the soul from how clever it was, and I don't think that'd have been possible if the song specifically HAD to be about electric types and use the electric Miku design since that not only directed the theme but aesthetic and vibe the song should give off as well. We couldn't have a cutesy lovestruck Miku song from that design.
In the meantime we have plenty of amazing fanart, at least. I'm looking forward to the other songs. Are there going to be 17 songs too? Cause there are so many vocaloid producers I want to hear get in on this (OSTER project and Nayutalien are sorely needed in this)