Harmony - Troop Symmetry

While pondering the "machine mastery" skill, an idea came to mind: The ballista and tent branch is undoubtedly useful, but how many will actually invest in the catapult branch? It's only useful during a city siege, and even then, you can easily do without a catapult – archers and flying units are always available (plus the hero's magic). Oh, and the cart becomes "immortal." Perhaps the "runic machines" perk should be positioned as the culmination of upgrading the catapult branch and increase the initiative bonus to, say, "+5"?