@Glowingworms
A quick watch of the voice, x factor or even if you go round cruise ships/ pubs, west end singers shows thousands of really really good singers that are better than 90% of "stars" but are also just chronically boring, and don't have an edge that make you want to buy their singles or listen to whole albums or seem to "musical theatery"
Nail on the head there. For the real "stars", it's never really about the voice as most are pretty ordinary (or augmented by backing singers/tech). The voices on background singers on Disney films or in theatre musicals is often far superior in terms of vocal ability, range, etc., but the singers don't have the "extra" presence to make them a story, or some image surrounding them. Having a excellent producer, songwriter, etc makes far more of an impact than vocal ability.
Personally, I think Madonna was grossly over-rated, also Tina Turner, as if you actually analyse their vocal range/ability, it's pretty ordinary and nothing special. But in both cases, there was an entire industry behind them to launch/relaunch them, carefully planning and marketing the back story, carefully choosing the songs to record, carefully choosing live performances, carefully choosing costumes for the "right" amount of risque, special effects, etc. Everything is stage managed to promote the singer often to make up for their lack of vocal ability. Of course, someone who literally can't sing or is tone deaf is going to struggle, even with an entire promotion industry behind them, but there have been "singers" who have basically talked or shouted through their songs and still be highly successful.
It must be soul destroying for the ones who do have a brilliant voice but just can't get the breaks and can't get noticed.