I think it would be beneficial to expand it and add a few new hotkeys in Find Units tab:
Find All Melee Cavalry (including units like Coyote Runner)
Find All Ranged Cavalry (including units like Eagle Runner Knight)
Find All Melee Infantry
Find All Ranged Infantry
Justification:
I played a few games as Lakota recently. I had o lot of units on the field: War Chief, Axe Riders, Tokala Soldiers, Bow Riders, Rifle Riders, Wakina Rifles and even a few Cetan Bowman. It was quite a headache to group them quickly. Proposed hotkeys will be very beneficial to have and should not be difficult to implement
I suggest just only need to add a hotkey: to find all type"s" of the units of currently selected units.
And this can directly solve all the OP’s problem once for all.
For example: OP can select a bow rider and a rifle rider. Press the hotkey to add all the remaining bow riders and rifle riders on the battlefield to the selection. Add all these ranged cavalry to the same control group. Problem solved.
I have suggested this feature several times. So far the current “select the unit of the same type” hotkey can only select “one type” of the unit no matter how many types of units you currectly select, making this hotkey not practical at all.
Many Civs, especially the civs need to mix multiple types of units to fight, require this feature urgently.
For Pro players who can micro army efficiently, it might not be a big problem. But for Average and Low skill players, this might cause some civs way more difficult to learn then other civs which only need to spam 1~2 types of units, despite all civs might seem to be balanced on the data.
So please, consider adding this feature again, thank you very much.