I have to wonder about that. Ahmadiyya sure has a reputation for being more peaceful than Shia and Sunni, but it is not like those two orthodox sects ever openly embraced violence.
Of course, it is not like they could ever have grown nearly as much had they openly and consciously made such an option for violence. If for no other reason, because other communities would no longer hesitate to oppose their growth.
The Ahmadiyya are certainly somewhat more ecletic in their appreciation of other creeds than the Shia and Sunni, but from what I have seen the perception of their contrast to those orthodox sects is greatly exagerated.
Shia and Sunni are peaceful in communities where they are a very clear minority as well. It remains to be seen how significant the doctrinary differentiation of the Ahmadiyya (who are a minority everywhere, in no small measure because the Muslim countries will not accept their doctrine) would be if they became more of a demographic presence somewhere. I have to admit that I am not optimistic.