The fact that turrets are rather fragile is a little concerning. If the turret cap DPS is balance target to be 2x (or was it 3x?) of the balance target of a cap of the corresponding fleet ship mark, shouldn't their balance target for cap health be >1x of the balance target for fleet ship cap health? It doesn't have to be the same magnitude, but turrets being glass cannons is a bit of an oddity.
I think it depends somewhat on the turret.
Some turrets for sure need more health. The flak turret is meant to be a brawler turret meant to camp at a wormhole and give and take a licking in return for low caps and range. However, it has less cap hp then a laser turret which is effective against more things, has no negative multipliers, and much larger range. To conclude, the flak turret is suprisingly squishy.
However, most of the time, for me, I'd rather turrets be glass cannons. They have no mobility, so I need them to dish out as much dps as they can before their targets go out of range. Usually they get off two salvos due to their superior range before they start getting hit so it works out, and some like missile turrets almost never get hit.
DPS > Health for turrets then, for turrets can't follow the action and can be set in advantageous locations.