As far as accuracy is concerned, single BA's seem to come the closest with the fewest compromises compared to multi-BA's, dynamics, and even most full-sized cans.
Focusing mainly on single vs multi-BA, there don't seem to be many multi-BA's without compromises in FR, IR and delay. There is a lot of room for subjectivity here, but by the numbers it seems that single BA's like the ER4S do better than everything else out there when accounting for an accurate diffuse field reference.
So if accuracy is the goal, are multi-BA's totally worthless to this end? It certainly looks like nothing short of electrostats can compete.