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I’d suggest post mount is similar to square taper cranks. Both systems work but are frequently fucked up by users rendering and expensive part useless. It’s easier to find a better interface than to eradicate the problem of human stupidity.
If a component is likely to be broken by incorrect installation make it the cheaper part that fails. So with the change from square taper to two piece cranks it went from the crank arm failing to the cheaper BB failing if installed poorly. With the change from post mount to flat mount it is now the caliper rather than the frame that is likely to get damaged.
Your frustration is acknowledged but I think it's somewhat misdirected.
I'll blame frame and forks producers and hamfisted mechanics not post mount standard.
Also lest we forget, IS standard is one of the main benefactors of post mount as it's just an adaptor to fit between the former and latter.
Hamfisted mechanics buggering up your flat mount calipers? Possibility too...