Ok I think I lost the point here somewhere along the way, please restate the point/request unless I have it right below:
Are you saying that you can't have a successful 5e game that doesn't have all the core 5e classes, and that's why you couldn't do a modern Dark Sun because you'd have to cut out a lot of the core 5e classes and fantasy tropes, rather than "here are ways that you can fit everything in the phb into this setting, even though it really shouldn't belong?"
Because I
think that I might know of a couple different Kickstarters that did this, to different degrees, but I want to make sure I'm understanding the point first