You do know that their cap is proportional to AIP?
Are you thinking of the
Dyson Gatlings? You are correct about those, but GeistenHaus is asking about the
Laser Gatlings - a bonus fleetship.
As for the original question, Laser Gatlings have a base cap-DPS of 160,000. This is a major increase over the Fighter's base cap-DPS of 98,000. So, in the general case, Gatlings don't look too bad.
You are right, however, that when you compare bonus-DPS, the gatlings lose out. There are also a lot of problems with the high-cap, low-hp ships in general, and there has been a lot of debate on how to solve these issues. No one has yet managed to come up with a solution.
So yes, starting with Laser Gatlings is not as advantageous as starting with, say, Spire Blade Spawners or Zenith Bombards.