Alan, you're preaching to the choir.
In the past I've had floors levelled using 'gypcrete' or a gypsum-rich concrete. This is an exceptionally strong, waterproof mix that also flows very well; I think its as fluid as water when first poured. It can be sloped, levelled, and finished to an extremely close tolerance. I'm not even sure there is any sort of aggregate in it.
As for the owner's quirks ... this experience is highlighting the differences between a pro and a DIY. It's underscoring the need for having a plan and actual job management. Instead, we're sort of drifting along.
One factor in the equation is a desire to just throw it back together, just well enough to last until the place is sold (in some undefined future). Pass it along to the next guy.
It's also clear that these same exacting, eagle-eyed customers have absolutely no shame in hiding all manner of hackwork behind the panelling. I guarantee they'd have a fit if a contractor tried doing the same thing.
