proposed forcing mechanic is that atlatl has reduced effectiveness in range when firing upward, compared to arrows which could more readily inflict damage on an object at greater height

implies increased dependency on roosting birds for game meat pervasively in the south (where atlatl use ceased immediately), seasonally in the north (where dual use continued for centuries)

for PvP events I suspect the warclub & shield was still the preferred kit

The fast transition suggests there was a strong pressure to switch, which probably didn’t come from animal hunting patterns.