Harmony - Troop Symmetry

SRD, is it possible to make it so that with the following perks:

ballista --> rapid-fire ballista
the player cannot obtain fire arrows?

Yes, it's possible if we move fire arrows to a different branch - it's already done that way - fire arrows are in the catapult branch, but the problem is that when choosing between the "fire arrows" and "ballista" perks, it's more advantageous to take the latter rather than the former.
In short, we need to add some kind of bonus to fire arrows so that there's a reason to take it, and not just the "ballista" perk.
I'll leave it unchanged for now, as good ideas on this topic can only be implemented using scripts, which I don't know how to use. After the first versions of the mod are released and the balance is refined, I will contact people who know about this - maybe they can help.