First off my bad for such a late reply. Meant to get back to you earlier but then forgot about this thread after a while.
I think we're on different wavelengths in this discussion of the greatest singers. To me that term implies something more than hitting the right notes when called for. I'm not sure how familiar you're with Billie Holiday, but she never had a big voice even in her prime, nor was she ever a technical wizard on par with Fitzgerald or Sarah Vaughan. Where she truly reigned supreme was in her matchless gift for imbuing each and every word and note with her soul (for lack of a better word) that made her listeners feel like she had nothing left to bare. For that reason alone the likes of Whitney, Mariah, Celine and Adele can't even begin to compare to her despite their superior vocal prowess, and not even an indisputable goddess like Ella or Aretha is her equal, because singing for Billie was more than a calling - it was her lifeblood, the one thing that kept her alive even when her tragic private life had hit rock bottom.
Obviously Freddie wasn't a transcendent genius comparable to some of these names, but to me the kind of "stage presence" as we saw in his famous Live Aid performance transcends mere entertainment. Feel free to correct me but Dio despite his bigger pipes never commanded his audience like that, and you'll be hard-pressed to name another who did, because Freddie's was such a rare gift. You mentioned MJ as his only possible superior in that respect and indeed Mike's stupendous talent is another good example. When you saw the Moonwalker about to don his trademark fedora for "Billie Jean" you sat up and watched, because you knew you were about to witness a show like no other. It wasn't a life-changing experience, no, but you could say it was life-affirming to see such a perfect mix of song, dance and showmanship. (And I really emphasize the "song." Try listening only to the
famous bass line of "Billie Jean" if you haven't already - it wasn't until I did that I realized what an extraordinary record it is.)
OTOH a better voice doesn't necessarily equal superior artistry. You might recall Madonna's singing improved by leaps and bounds when she prepared for her role of Eva Peron in Evita, and that carried over to her justly acclaimed (if overrated) Ray of Light which followed. But while she was singing better than ever before there was a certain distance to her songs on what was an undoubtedly serious album, as if she was trying to channel her newfound religion (I'm guessing you remember her whole kabbalah nonsense phase) through her new "serious" voice. Compare that to what was deemed her first serious album, Like a Prayer, which was full of fiery passion, irreverent piety and plain joie de vivre. Sure, her voice was still amateurish compared to its post-Evita cousin, but if you ask me her "singing" on the title track and "Express Yourself" dwarfs any of her trained vocalizing on Ray of Light. If that doesn't make her younger self the better singer then why are we focusing on these names in the first place, when there are literally thousands of less famous performers across the the globe who can fulfill the same duties of vocalizing to more exacting standards?
Hopefully you see now where I'm coming from. I don't wanna get too sidetracked here as we're supposed to be judging singing after all, but when we're talking about the greatest singers I need more than a little evidence of said transcendence on their part beyond having a great set of pipes which don't interest me as much. The latter while impressive are a dime a dozen and should in the end serve as a complement to the expressive powers of an artist, provided that he/she's an artist in the first place.
BTW even the best-trained singers can damage their voice and be forced to cut down on their activities if they're not careful. You may know this already but it's been said that Callas' voice underwent an earlier decline than most because she took on too many heavy roles at the beginning of her career.
Yes, one's background certainly has much to do with how you digest any subjective experience. As you may recall from that other thread I still watch the MLB postseason at least in part because baseball is the sport I grew up watching and playing more than any other. I do think I'd still be a baseball fan without such firsthand experience (I actually like that it's slow and thus offers respite from the breakneck pace of modern life), but probably a very casual one at best.
And one's politics/worldview has a significant impact on your artistic choices, too. I've never cared much for authority and in fact if pressed to name one thing I hate most about (East) Asian culture I'd say its often blind respect for the elders that the youngsters are expected to have. So naturally I've always been a voracious consumer of cultures of all nationalities and backgrounds, and any time I encounter something new I generally see that as a good thing. Those with stronger inclinations for structure and discipline, OTOH, probably aren't as tolerant of arts and cultures alien to them. Not saying your father falls under the latter category, of course.