John,
Not trying to be a smart ass but I believe you are comparing two completely different types of weapons.....at least as employed by Native Americans. The Atlatl is a projecting weapon and a spear (not a javelin) is a thrusting weapon. While the one acts much like an arrow in projecting the lethal point from stand-off distance, the other is/was used to inflict large wounds; repeatedly, and at close range.
An example would be the great lakes tribes who regularly hunted both Moose and Buffalo, and they were not horse cultures. They did so by being smart. One way was to run or heard these animals into deep snow fields where they foundered and the hunters could run up beside them on snowshoes and stab repeatedly, then run on to another. Another way was to drive them into water where hunters in canoes could paddle up to the swimming animal and again stab repeatedly. The system is very similar when buffalo were run over a "jump" and then finished off at the bottom. The spear is the enduring weapon while the atlatl was replaced by the bow.....even the Inues' harpoons (and throwing stcks) are still like spears more than atlatl's and used because you cant get within arms length of whales or walrus etc. and so the harpoon head requires a very short throw distance for the harpoon head to be delivered, but the killing lance is hand held.
Survival and subsistence hunting has nothing in common whith white guys sport hunting. One requires the dead animal without injury to the hunter, we do it for sport and invent reasoning and rational for "how to do it".
Sorry for "droning on" just wished to point out that the atlatl, spear, javelin, and lance are all different weapons so I do not believe one can be compared to the other without being taken in context of their intended purpose.
rich