Dont forget sten! He has no horns.
Sten really doesn't apply to a discussion about the Qunari that do have horns. I know he is an anomaly in Qunari society -- hornless Qunari being meant for great things -- but in the context of the discussion about the Qunari that do have horns he's rather irrelevant.
As for varied, we have only two types to go off of from DAII. Concept art is nice but it's not always indicative of anything and often the final result is different. I'd say that the Arvaarad's horns and the Arishok's horns are only different because of length and that if the Arvaarad let his grow out they'd form to be eventually the same as the Arishok's.
Of course, we don't know the horn growth patterns of the Qunari in general, so even if it is possible for them to grow the same way their horns could be like our hair where it's all relative to the individual.
Still, whatever the case may be, I just think it's odd as hell to have such a sudden shift without warning. Not that it's necessarily a bad thing as I think Iron Bull looks badass.
It's just odd.