I’d go right with trying the DN. Snail pace is only relevant if you’re draining energy, if not, simply increase warp factor. And unless I’m mistaken, the dreadnought wouldn’t be any heavier than the Hydra.
A development I’ve been working on (on paper, I never got to actually test it on the field) was a line formation. Basically, we have a wall of five DNs that coordinate movement very closely and 3 CMs for support fire. The idea is to provide an effective approach to defensive scenarios in which the only way to win for other groups would be aggro-based tactics.
Now, about roles. The scout would be alright. Her ideal role is, in fact, a tank. She absorbs damage no other class can even without shields. That doesn’t rely on energy but on the internal layout. I’m more concerned with the CM, as she would have effectively endless ordnance. Even more so with the TSN stronger homings.