Cooper can't be a loner? or easily get to PDX without being noticed, or traced?
The FBI admits it's the most probable place he jumped, but since no data has surface we can not determine whether the path is correct, or the timing of the jump. none of the other copycat hijackings had anything to do with wild rides getting away from the dropzone. the FBI now believes it's possible the jump was further south, which brings you closer to the river.
How hard do you really think it would be to parachute and leave the area? he had a good head start on them. Tosaw believes he went into the river, he's not the only one who has this theory. lets not forget about the path possibly being more eastward into the Washougal area, or R99's theory of the path westward?
Cooper tried to get the stairs down very early in the flight, do we automatically discount an early exit? if you don't, then you left your boys behind where they thought they should of been to pick him up?
Did he know the plane would fly over Ariel, and near the dam? I don't know. the known evidence doesn't point to him have any idea where he was. did he know the best case to jump from the stairs, freefall, or deploy off the stairs? it's all speculation due to not knowing the knowledge he had.
Nobody ever thought getting off Alcatraz could be as simple as catching a ride on the same boat that brought them to the island. it sounds plausible, is it true? time will tell. for years they have tried swimming across the bay to prove it could be done, when it's possible none of that matters what so ever if the new theory turns into fact.
sometimes things turn out a lot simpler than we make them out to be