The action economy is the central problem with henchmen and followers because an extra action (even by a weaker character) is an extremely powerful ability. Animal companions, along with summoned monsters, have the problem that -- if they get their own actions -- they need to be almost uselessly weak or prohibitively expensive to be balanced against other character abilities.
I'm not sure what the answer is. I suspect that animals and followers are going to need to have an on-going monetary cost -- something that makes them like a different type of magic item. Then the character abilities that allow PCs to improve their morale (and maybe hire them more efficiently) can be compared against character abilities that create magic items.
All of this would be optional, of course, but it seems to me that worthwhile companions and followers have to be treated as a form of semi-expendable treasure. In other words, they are a valuable thing that exists in the gameworld and not an entitlement from a character ability. (That wouldn't go for familiars and other non-combat animal companions -- those are weak enough that they make reasonable character abilities.)
-KS
I could see this being balanced by level.
Combat cohorts will not be available at level 1. You'll get them all level X (or upgrade your noncombat cohort to combat worth at level X).
At level X, your battelbulter/ninjamaid/petbear/T-rexBFF/combatbird/golembuddy/childsidekick has crappy HP and just one attack. An equal level character would clobber it. And you + it would have to be made wear it won't be stronger than a character of the same class with a different theme.
A 6th level fighter (beastmaster) might get 3 attacks with his sword for 1d10+4 damage or from his bear form 1d8+6
A 6th level fighter (slayer) would get 3 attacks with his sword for 1d10+8 damage and deal 2d10 extra damage on critical hit.