To be fair, Starmie is a glass cannon, especially when it comes to physical defense, and Hitmontop is a physical attacker, so it's not completely unfeasible, particularly if Hitmontop uses normal type attacks. Also, Weezing is one of the best tanks in the game, which incidentally is exactly what a good poison type should be.
That reminds me, if you want to train up a new pokemon from scratch, I'd highly recommend Slaking. Teach it hyper beam, give it a silk scarf and it'll easily one hit KO opponents that are several levels higher. Base physical attack stat of 160 is a wonderful thing.