Here is my suggestion (yes it's a rehash of an old one but that is several years old and the tech is more available for it):
Provide the leadership feat as a choice for those that want it. What it would do is this:
The henchman would mostly act like the pet for the Artis and the druids.
It would start at whatever level you took the leadership feat at, and gain levels as you did, like the pets do if you go straight class.
As the henchman leveled you would have full choice of its feats. Enhancements would be similar to the pet enhancement lines.
If it is a caster you have the choice of at least 2 of its spells per spell level.
The player has full access to editing the "hireling" hotbar with any/all of the abilities available to the henchman.
You can view the henchmen's inventory screen, and can give them equipment just like you can with the pets. The inventory would most likely be limited to armor/docent, 2 weap slots. Yes they could be weap/shield
The henchman would count as a full character for the purposes of dungeon scaling, but would still not be allowed in raids.
While the henchman was active, you would not be able to use a hireling contract of the same class, unless it was a gold seal hireling.
If all of this is too complex to program, then the feat would act this way:
The feat would have 4 subfeats: summon caster, summon healer, summon rogue, summon melee.
These subfeats would summon the hireling contract of your level for whatever subfeat you clicked. For example if you are level 13 and clicked summon rogue, it would call the level 13 rogue hireling. These would only be able to be called at the entrance to a dungeon like normal hirelings.
Picking one of the henchmen would lock the other classes out for a cooldown TBD. Alternately, you would pick what kind of henchman you could summon when you choose the feat. This would be a permanent choice.
Any and all feedback is appreciated!