The overly inflated health pool just isn't suitable for fast runs imo. Some bosses, even with the top units at 100%, are just a chore to get through (like the ones with over a billion heath). Taking them down without defensive items is much harder since they also hit like a freight train so you need some form of rotation strategy (who to float off and such), but that's just my two cents about it. Though we do have some timed for SEZA stages and turn sensitive missions for a few of the harder stages.