I think as much attention needs to be focused on the pilum as on the penknife the Romans used. It wasn't just something to "even the odds" a little before the serious stabbing part, it was crucial to a successful attack. A well-timed volley would seriously dent the enemy's line, and then it wouldn't really matter what your men were armed with when they rushed through the openings created. As long as it poked the bad guys and they fell down, good enough.