Those seem like reasonable explanations utill you consider that a bow can last many years under constant use but arrows break more often. Especially when when hunting big game. Plus most of the blunts are at least an inch round and a bow limb would be to thin. But it may have happened and maybe that is how it started. I know that the Sweedish are said to have taught the Iroquois how to make splint baskets so that makes me wonder if Europeans encouraged them to make arrows from split timber, either through sharing techniques or by introducing metal tool to make this procces more efficient.
The advantage that I see and surly that the Eastern Woodland people saw is that you can make many different durrable arrow heads from hickory. Most shoots that I know of around he in PA have pith and you cannot make a sharp durable self point(although that Camanche design looks good). With split timber you can make self points, self wood broadheads, and blunts.
That is just my thoughts,
Mikael