Every promotion line is useful, so are most units. The problem is picking the wrong combination.
For example, the best defender code somewhat overvalues first strikes. If you promote the majority of your units to Drill (e.g. to decimate overwhelming numbers of obsolete units without being worn down, or as efficient cleanup units after you lead with siege units), Formation is the only useful counter promotion for stack defenders.
Against units not immune to first strikes, your generic Drill units will defend first anyway. Making counter promotions work on the offense can work but you need to know what you are doing and it isn't worth the hassle most of the time.
Similarly, you need either enough siege units or dedicated can openers in the form of City Raider troops, not both. If your can openers are good/cost-effective enough (e.g. Praetorians, Samurai), a few catapults will pave the way with bombardment, possibly a few sacrifices to make the combat odds favourable. If you don't expect any survivors, they are more efficient than Trebuchets for dealing collateral damage so you have no need for those.
If, however, you intend to throw Trebuchets at the defenders until they are almost dead, you don't need CR-promoted Macemen to clean up; anything will do, units with first strikes may even be better. Here you want a well-rounded force of stack defenders because your Trebuchets are disturbingly fragile. Macemen can be part of that since they are good defenders against Pikemen or siege units. If they will have better odds against a single strong defender than a Trebuchet, so be it... but you don't need to promote them for that job.
For example, the best defender code somewhat overvalues first strikes. If you promote the majority of your units to Drill (e.g. to decimate overwhelming numbers of obsolete units without being worn down, or as efficient cleanup units after you lead with siege units), Formation is the only useful counter promotion for stack defenders.
Against units not immune to first strikes, your generic Drill units will defend first anyway. Making counter promotions work on the offense can work but you need to know what you are doing and it isn't worth the hassle most of the time.
Similarly, you need either enough siege units or dedicated can openers in the form of City Raider troops, not both. If your can openers are good/cost-effective enough (e.g. Praetorians, Samurai), a few catapults will pave the way with bombardment, possibly a few sacrifices to make the combat odds favourable. If you don't expect any survivors, they are more efficient than Trebuchets for dealing collateral damage so you have no need for those.
If, however, you intend to throw Trebuchets at the defenders until they are almost dead, you don't need CR-promoted Macemen to clean up; anything will do, units with first strikes may even be better. Here you want a well-rounded force of stack defenders because your Trebuchets are disturbingly fragile. Macemen can be part of that since they are good defenders against Pikemen or siege units. If they will have better odds against a single strong defender than a Trebuchet, so be it... but you don't need to promote them for that job.
