It's all good man!
I did actually mean to get back here with my findings, which were exactly what you just described above.
I'm not sure any of this tech will ever be perfect for splitting to stems, especially for vocals (unless it's a very open, acoustic track maybe) but actually 'rebalancing' I.E turning a vocal up in context of the rest of the track, or turning the bass up, work really well. Because obviously it doesn't reveal the discrepancies.

There's also Accusonus Rythmiq that does this. Much quicker than iZotope.