Only speaking for myself, when I flew a cannon escort, I usually sat in front of the target and rarely got bothered by it. If I did move, it was creaping forward or moving in reverse. Never had that much problem dying to anything. If I did get tagged, I'd do a quick evasive, hit my heals, and come back in.
For full disclosure, I was an eng character, with full cannons and usually attack pattern beta, cannon scatter volley, and torpedo spread for the first volley. I also managed to survive the plasma torp spread of death from the Borg, and I was in a defiant for all of this.
Also, pretty sure that escorts that fly around get more defence than a cruiser since they have a higher speed.
Ironically, the best match up of weapons to ships would be to have escorts have beams, since they should have to manuever around to survive and beams lets them do that while still doing damange. And then Cruisers should have duel cannons, since they can get up close, sit there and pound away at the enemy.