Hello, new here in the forums but not new to the franchise.
I'd like to apologize in advance if I'm maybe necroing this thread (not sure what the threshold is), but maybe I could throw in a suggestion loosely similar to the one RoamingCharges made.
Basically, subtypes. In this example, that button used to pick between types could, if you right clicked it, be used to pick between subtypes (actual troops) through a drop-down that would allow you to check or uncheck one or more of them at a time, preferably with a "toggle check all" on the top of it. So left click would still switch between types, right click would go for subtypes.
So let's say I had the following infantry:
Imperial Recruits
Vlandian Recruits
Sturgian Linebreakers
Battanian Falxmen
Sergeants
Legionaries
I go to group 5, I pick infantry. I right click the sword icon I picked, a different dropdown appears. I check Imperial Recruits and Vlandian Recruits, click "Done".
I go to 6, Infantry again. I right click and check Linebreakers and Falxmen. I now have my formation intended to break a shield wall or circle formation.
So in the end, 1 is left alone as a general-purpose/shield-wall infantry formation with the Sergeants and Legionaries, 5 is my Recruits group I may wanna back away and save for looters and 6 is for shield breaking.
So instead of being able to mix horses with infantry or anything similar like you were saying in that quote above (and potentially breaking the game), I am branching out a type into subtypes through a dropdown list that's only as long as the existing number of troop types in the party.
I think there's definitely a place for the current OoB and I don't think it's a bad system. It's simply missing troop type formations, which makes a lot of people (myself included) feel rather blue-balled over a cherished feature that existed ever since the Warband days, maybe even earlier than that.
Apologies for the wall of text and thank you for taking the time to read this. Eager to hear your thoughts!