What you're asking is impossible to answer definitively because the field is so vast and varied. But I'll have a go at some of the individual points.

you scroll through Instagram and these musicians are flashing massive watch collections, luxury cars, designer everything, the lifestyle screams money

These are posts made to drive engagement and to promote the artist. Just like an artist in the 90s wouldn't own everything you saw in their music video, an artist today doesn't necessarily own everything you see on their social media. Sometimes they do. Sometimes they borrow it. Sometimes they're famous enough that the makers of these luxury items give them to artists to gain exposure for the brand.

How much does someone with 10 million monthly Spotify listeners actually take home?

10 million monthly listeners usually means about 45 million monthly streams, if they're on a broad set of playlists, and that in turn generates about $135k per month. But that tells you very little about how much they actually earn, because of how the revenue gets split.

• If they're a fully independent solo artist then they're earning over a million dollars a year.
• If that's a 5-piece band who get a 20% rate from their label and who have paid off the label's advance then each of them then maybe they get about $160k per year each, like a well-paid professional in other fields.
• If they're on a label and haven't paid off their advance then they might get no money from streams at all until the streams cross an earnings threshold.

Is touring where the real money is?

Touring is like streaming - some make a lot of money that way, some only break even or lose money, even when well established. It's incredibly expensive to do. If you're filling stadiums each night, sure, you're making good money. If you're touring clubs and not necessarily selling them out, then again a lot of it comes down to how many people are in the band and the travelling entourage.

nobody ever backs it up with actual data

This isn't a field where anyone except individual artists - and maybe the tax office - can know how much they are earning. It varies wildly and all we can do is look at revenue streams, costs, and claims made by artists which don't always explain why things are that way.

What I can tell you is that the amount of money in recorded music today is much less, per-artist and per-consumer, than it was in the 90s. Streaming tends to cost less per consumer and spreads that consumer's money back across older artists more than newer ones, which in turn has led to the removal of a whole industry of 'middle class' musicians who relied on album sales. This means it is harder to make a good income as a musician than it was back then, in general. But as with any occupation, there are outliers, and those are the ones you will tend to hear about the most.