I've just checked now and you're right, particles appear to render the same as other billboarding entities. Sorry about that
That's untrue; particles like block_marker or explosions correctly billboard to the player when rendered.
block_marker
@Brain - what? It clearly isn't a dupe of MC-259915.
That bug is about item display interpolation. This is about entity AI breaking when being ridden by an item display.
I've just checked now and you're right, particles appear to render the same as other billboarding entities. Sorry about that