No, your memory is spot on. I also eval'd dozens of ARM (and some x86) SBCs for embedded use back in the early/mid-2010s and most of the BSPs were awful. You'd be locked into some ancient several-year old Linux kernels and documentation (and even actual hardware support) was often buggy/incomplete. God help you if you need to customize the boot/spin your own (Yocto was still new then, I assume life is a bit easier now).