As Shield Tech or any form of tank spec your dmg will be laughable, get used to it. If you want to wreck faces go Pyro, that spec dishes some serious numbers. Still, utility is nice for those tanking specs, but don't expect to dominate. If you pair up with a healer the pair of you will be difficult to kill, and you can hold objective nicely, but killing others ain't gonna be easy.
So, killing people = Pyro.