It’s simple. Currently we have two options: we either raise a troop’s level by 1, or we spend as many souls as we can to level up the troop, up to either what you can pay, or to the troop’s level cap.
EDIT: I’m aware that if we don’t have enough souls to raise a single level, we see how much it would cost and what the buffs would be for the troop at its level cap.
What I’d like to have is an option, maybe with up/down or left/right arrows, to choose how many levels I wanna go up with that troop. That way, for example, if I wanna level a troop to level 7, I’d be able to see how much souls total I’d spend, and what attributes would go up (just as it works with the “max level” option).
This is especially useful if I wanna raise a Kingdom’s power, looking for efficiency on how many souls I spend. Doing 1 level at a time works, but it takes way too much time.