It's too easy to build a ship that is impervious to all weapons (except Electro-bolt) by using a few shields and PDs.
Here is my annoying Stunner ship that seems to hold its own against all other ships above and slowly takes out the other's gun. It can take a while to win though...

There should another rule or two, like cost or shield/PD limit.
Edit:
I realize I only play vanilla right now. So I'm sure some mods make this more interesting.