Sorry, but I disagree. Anti-camera scanners and anti-vaxxers have nothing in common and your comment is flawed logic. The few Flat Earth Society members I've met were highly intelligent people who were amusing themselves with an outdated and as we all know, quite absurd theory. My disapproval is saved for those small fundamental minds who still believe our planet was created in seven days or those selfish types who believe it's okay to trash the world in the name of lifestyle.
We ex-camera-scanners have at least tried and tried and all run into the same problem and eventually given up. You write that the problem was something I did - respectfully, please kindly take the time to enlighten me as to what that was, if you think you know.
You posted three good images, all negatives, not slides. I had few contrast problems on camera-scanned B&W films (I recall I did have to slightly underexpose them to cut down the contrast, which affected the shadows, but never mind). As for slides, eh!! It may be that more modern cameras (I used my D700s) are programmed to handle scans.
'90s technology? ha! Doesn't this term sum up every affordable priced scanner on the market today, excepting (maybe) the super expensive whizzbang machines used by prolabs, government archives and museums? I would happily buy a Hasselblad scanner if I had the money, but on a retirement budget I have to make do with a humble Epson and an adequate if not entirely user-friendly Plustek. But then it may well be that even the 'blad scanner is old technology - I've not really looked into this so I'll say no more.
Come to think of it, are almost all if not all photo scanners not jazzed-up 1990s equipment with a few new bells and whistles, mostly in the software? I try to think of any really new innovations in today's range of dedicated photo scanners or flatbed scanners set up to do negatives and slides as well as paper prints, but for the life of me I can't. Any ideas here?
Using my older scanners I can produce images that satisfy my requirements and those of the few publishers and magazine editors who still buy my images from the 1960s, 1970s and 1980s. I would be happy to invest in any new scanner technology made now but sadly, my clients nowadays pay me less for my photos than they did 30 years ago, so the cost factor is too high for me.
As for camera scans, I am in favor of anything that will make our lives easier - just not at the cost of expensive gear or overkill processes. I no longer buy anything made by Sony but the 60MP Sony a7R IV scans you mentioned would surely be huge and I would be have to allow too much time resizing to smaller dimensions, so no go there for me.