I'mma make this simple. The dreadnaught is a fickle beasty. It CAN work, if flown properly with the right equipment. Not many people do fly it properly, which is why so many people say it's underpowered.
I say it's a niche ship. No matter which way you fly it, it needs too be flown with a fleet. Find a group of people, and stick with them, learn how the beauty moves.
I personally recommend the Hakashin build. I've flown it myself. The only downside is it's primarily made for tactical pilots, meaning if you've specced into something else, you're btter off with a different ship. Use the thing as a giant sniper rifle. Put as much firepower downrange as possible, meaning cannons and CRF 1. DEM can help, but I don't ever notice huge improvements too firepower with it. So long as you stick as many of the best phaser relays you can get your hands on into the tac slots, and use a a properly timed bombing run, this thing will eat most weaker hulled starships for breakfast. If you've got a stronger hulled ship your trying too take down, have your team munch on it for a while, then come in and do the same thing to them, decloaking and snapping their hull in two with the lance.
When I used this build, even on mediocre equipment, I would often break through smaller weaker cruisers. Tor'Kahts didn't stand a chance, and escorts were piecemeal prey. I often saw 70-80k + alpha strikes from the lance.
I AM THE HARBINGER OF HOPE!
I AM THE SWORD OF THE RIGHTOUS!