When putting together a fit, we all like big numbers. Big damage. Big ehp. Big max velocity. We want big. But big numbers can be misleading. And sometimes we don't understand those numbers as well as we think we do.
The above graph is taken from EFT, and it shows two identical Succubi shooting at a Suitonia fit Kestrel (faction warfare version). The Succubi and the Kestrel are moving in opposite directions, at full speed, which fits with how they would actually face off against each other. The Kestrel uses rockets, so he wants to mess with the Succubus's tracking as much as possible, and the Succubus wants to keep velocity high to minimise the Kestrel's rocket damage.
The red line is the applied damage of Gatling Pulse Laser II using Scorch, and the green line is the applied damage of Dual Light Pulse Laser II using Scorch. The fits are otherwise identical. The raw EFT dps of the GPL fit is 161, and the raw EFT dps of the DLP fit is 167.
Despite being 6 raw dps lower than the DLP fit, the GPL fit is actually applying more dps at every range up to about 9.2 km - past cold T2 scram range.
This is very interesting, but does it hold true in other common scenarios?
This second graph shows the same two Succubi, this time shooting at a standard buffer fit blaster Merlin. The Succubi are still in orbit, but the Merlin is moving directly towards the Succubi as it tries to close the distance and get into range.
Once again, the GPL outperforms the DPL out to about 9km, although the DLP is starting to catch up by the time we reach end of the GPL's optimal.
So, for the Succubus at least, we can say that unless you intend to fight at overheated T2 scram range, DLP is simply a poorer choice than the GPL, despite the higher raw dps.
Fighting at that range risks letting your opponent escape through manual piloting, though, and there are a variety of ships that you don't want to fight at that range. Examples would include larger ships, where you want to get under their guns so that you can grind them down, laser ships, who will project their best damage at that range, and long range turret fits, where you will again want to get under their guns.
On top of that, the GPL has a lower cap draw (useful when fighting under a neut, although otherwise irrelevant for the cap stable Succubus), and lower fitting requirements. The difference in fitting is enough to upgrade us from a meta web to a T2 web, for example, giving us an extra 5% speed advantage.
Now, we have to be cautious when applying these graphs to other ships, because Succubus moves at 1,894 m/s with a T2 afterburner, dropping down to 852.3 m/s after the Kestrel or Merlin apply their meta web. Those speeds push the tracking on any turret.
On the other hand, the Succubus also gets a tracking bonus, which to a certain extent counteracts the additional speed. A GPL - raw accuracy score 308.125 - tracks nearly as well as a Light Electron Blaster II - raw accuracy score 438 - after the Succubus's 37.5% tracking bonus. So I would imagine that for many frigates with neither a speed or tracking bonus this relationship between the GLP and the DLP will hold true.
In addition, the webbed Succubus is still slower than an unwebbed afterburner frigate, so if your unbonused frigate ends up fighting something that has no web, the GLP are going to be even more greatly favoured.
There is one serious caveat, however. The point at which the GLP starts to go downhill is determined by it's optimal range. So if you have less than Sharpshooter V, that inflection point is going to start getting closer and closer to your target, and you will need the DLP in order to project damage out to unheated scram range.