Well, to be fair, postmarketOS isn't Android. For Android I've had tons of custom ROMs with no obvious hardware issues, mostly CyanogenMod variants, over the years. postmarketOS, though, tries to run stock Linux. It's a different ballgame.
The alternate approach is actually to utilize the fact that Android is relatively better supported and wrap Android components into a standard Linux userland, using a compatibility layer like libhybris with patched vendor kernels. It's pretty ugly but if you want Linux on phone now it's your best shot at a flagship experience.
> it's your best shot at a flagship experience.
Is the Librem 5 really that far behind still?
Well, I don't have one, so I can't say with great certainty. I did, however, have a Pinephone Pro, and the experience wasn't great for a few different reasons. The Librem 5 is apparently faster, but it seems like it's not that much faster, so even if the experience is better I'd suspect it's not ready for most people. I think that's a real shame because it feels close and the target they're chasing (usable daily driver) isn't really moving as fast as it once was, but compared to a very cheap Android phone, the relatively-expensive Librem 5 is weak in almost every dimension. I considered buying it anyways... but I know damn well I can't daily drive it yet.