I actually agree; battanians should have a main tree archer. The issue is that if I want to play with battanian culture, I obviously want to prioritize a strong archer backline with a solid infantry frontline. The issue is that it's not particularly easy to get noble units, and even worse, it's kind of random. It's difficult if not practically impossible to force a village to start spawning them, and with wars, villages get raided and it becomes more and more difficult.
In my experience, noble units are something you get other time to supplement your main army. Over time, you might gather more and more, but it's very difficult, especially in the early game, to really build out an army with noble units as a main part of your force. Sure, with Veteran's Respect it can be done, but you'd need to join a kingdom and run an army for some time before that's even an option.
And so given my experiences, it makes a lot of sense to give battanians some mainline archer. As of now they have a weird tree anyways with two cav units and three infantry units in the fifth tier. That's a very strange fact, especially given that their cav aren't particularly powerful and they are intended to be great with bows. Some tier 5 bowmen would be nice.
And obviously I realize I can grab archers from other cultures, but many players love to play mono-culture, and so every faction should be relatively inclusive to that fact.