The thing is, every PD gives you 14% damage, so you having a 24/18 build, as opposed to my 18/24, that means you gain 28% damage over me. Twenty-eight percent. Thats equivalent to 3 and a half points of powerstrike. On top of this though, you're also gaining an increase to your effective projectile speed, which increases your accuracy. Of course, that's offset by the wpf per pd penalty, but nonetheless still exists.
Also, I've been playing with 27/15 lately. My first map played with the build, with 70 people playing on na1, I went 16:4(after tking twice on the first round ending with 0:0:1 score).