hi dont mind me popping in, just want to clarify your wording, when you say "no plugins" on that one version, are your speaking of plugins/effects done *in* vocaloid 5? or the effects you are doing while mixing separately (i assume, in an outside program)?
there's definitely something your mixing that i think causes more of that 'fuzziness' as well but i'd suspect it lack of equalizer/equalizer being done wrong. the version without plug-ins still needs 'something' imo, and that would be equalizer. correct me if im wrong on any of those assumptions about your mixing though! (edit: will add i havent mixed with meiko much and sometimes it can be the limits of the voice imo but still wanna throw somethings out there)
your slapped together one doesnt sound that bad by any means, but i get whats being said. i feel like the vocal (mostly in the verse) that comes up behind the main vocal is a bit too... 'on top' of the main, in both versions and some sharper equalizing could help the main voice, along with possibly some kinda chorus flanger effect and maybe even a stronger reverb in some spots for the backing voice- its not bad to keep the voice higher in volume to be heard but those effects can 'distance' it from the voice it is singing behind a bit more.
uhh its hard for me to write this as i work very hands on lol, so apologies if thats a bit nonsese. im unaware what you use to mix too, which may help give me an idea of some limitations/possibilities...