> They say they happily stop writing halfway in the middle of a sector, and respond to power drop only by parking the head.
The old DeskStar drive manual (circa 2002) explicitly stated that power loss in the middle of a write could lead to partially-written sectors, which would trigger a hard error if you tried to read them later on. According to an LKML discussion back then, the sectors would stay in this condition indefinitely and would not be remapped; so the drive would continue to throw hard errors until you manually ran a repair tool to find and fix them.