Hoo boy. Just 12 hours ago on the duel server I said "inb4 tier list" and look what happens. Mind = Blown
I'll leave my 2-bit opinion though, based off of my limited duel knowledge;
Spark Shock and Search Snake are worse than Dive Missile, definitely. It is very difficult to successfully hit with the Spark Shock, and even if it happens, chances are you will not be able to chain hits, due to the fact that you were probably moving around whilst firing it. The Snake is beyond too easy to dodge, unless caught off guard. Even if caught off guard, the little damage it does is no threat. Dive missile, when fired, is like a beautifully aimed mega buster shot, very useful for hitting fleers, even those with charge kick. Just today, I got 2 duel kills with it (however, it was in dive man's stage, take it how you will). I am uncertain that the Missile is better than Saku and Stone, though.
I really want to say dust crusher deserves a bump up, due to its 3 hit kill. However, I feel like you may have it right.
Man, my favorite weapons look a lot crappier in comparison on this list now >.>