All of the examples linked so far sounds highly artificial, so much that I'm guessing part of the charm for the listeners is the artificial and robotic sound/voicing, so the producers make it extra so in order to giver higher satisfaction.

Is there any examples of songs out there going the opposite way, trying to use something like Vocaloid to make the voice and singing as realistic and human-like as possible?

Ai Dee by Mitchie M is famously tagged [Miku & Luka sing like humans] on the original upload, so that was an explicit goal. Of course, it may not sound as impressive today as it did in 2012, but it's a reasonable attempt.

You could make a case for SOOOO in https://www.youtube.com/watch?v=0OOWWNFTguY. I don't know if it's intended to be as realistic/human sounding, but portions get close.

Most vocaloid definitely leans into the robotic quality.

Which portions specifically? Gave it a listen and didn't find any parts that came close to not sounding robotic. Maybe in comparison to the other examples linked here, that one was better (but I'm unsure if that's actually true), but if that's state of the art, I'm not sure it really comes close to hitting the mark.

Definitely not state of the art as far as being humanoid, that would be the top level link.

It's also not particularly humanoid, just closer than most vocaloids I've heard. Going off of my memory of the song, it's more the intonation then the timbre that stuck out as being more realistic.

I'm afraid I'm not willing to listen through the song currently, I usually dredge up some stuff I'm not wanting to deal with right now when I listen to this artists music.

Vocaloid sounding robotic is kind of the appeal to me.