Just as a point of interest, most casualties in muscle powered warfare came after one side routed and were cut down while fleeing.
Yeah, but "most casualties" historically typically meant ca 10-30% of a force, unless you were fighting Mongols or Parthians maybe (poor Crassus). The opportunity attack already handles that fine.
Obviously if you have cavalry vs fleeing enemy infantry on open terrain then long term pursuit is
viable, but in larger battles a lot of enemy are still going to get away.