I love the D'd and it's perfectly viable to build it with a cannon/beam combination. It's a unique experience alright but you can get around it's monstrous turn rate by using even the Mk X Enhanced RCS consoles
Once to mess around back when LoR just launched and everyone was complaining about the turn rate (nice to see some things never change lol) I decided to mess around. I put some common RCS on the D'D, the two C-Store consoles and used Aux to Damp, EPtE, Omega and Evasive Maneuvers all while cloaked. I had that monster doing doughnuts around New Romulus with a triple digit turn rate. I got quite a few tells that day.
So if you really want to make that D'D turn there are ways.
My Romulan Liberated Borg character made it to Level 30 and beat the (old) Defense of New Romulus with the skill point bug.