This is something I was thinking about the other day. A set of small-ish ships that can pack some long-range heavy weaponry, but are extremely vulnerable at close range.
Like the NOD artillery units in the original Command and Conquer.
Agility between a heavy bomber and a cruiser, a powercore just strong enough to fire the heavy weapons, one or two mounts for the heavy guns, a pair of fighter turrets for minimal defense, and a fighter-class shield. No mines, no CD/Torp mounts, only a countermeasure slot.
The idea is that you get a couple of these things together with a wing of fighters/bombers to take shots at capital ships from 2-3k out. They would be quite vulnerable to anything that gets up close, but could provide a tactical advantage if used properly.
The idea is that they'd be much cheaper to deploy than a cruiser. Say, 10M base price plus the equipment price. Far cheaper to deploy than a 200M+ cruiser.
While the concept is similar, my idea is more about anti-cap defense than all-around long-range ownage. Picture a Bazooka rather than a Howitzer or tank. The guy running up with the rifle is going to do more damage to this thing than the other two.