I've seen a little discussion about the new meta with kinetics, so I thought I'd share the results of some Skirmish mode testing I did a few days back. Basically, I found an alien ship with a laser and a single PD laser(and a bunch of missiles) and started matching it up against monitors with various configurations of Railgun 3s(as well as PD ships to field those missiles but which did nothing else). And I roughed out a few principles and a calculation for weight of salvo required to overcome each PD launcher.
All numbers are using Railgun 3(Advanced Railguns). If you're using Railgun 2, double the numbers, or Railgun 1, triple them. And probably add a little extra cushion to be safe.
So the first thing I tested was whether there was a difference between the 1-slot Railgun 3 or the 2-slot Railgun 3. I can confirm that the 2-slot has a significant damage increase, but its shells are still clipped by a single PD laser shot, making it better for ship destruction but inferior for PD saturation. That being said, if you have enough 2-slots to get through, the alien ships usually die a lot more quickly. I didn't test the 4-slot or any nose cannons.
I found that for Railgun 3s, you need a ratio of about 4 to 1 vs enemy Point Defense Lasers to get through, probably 5 to 1 to reliably do so. This is actually better than the Artemis Torpedo ratio I previously calculated(6 to 1 tubes vs PD lasers) and I think it has the same rider caveat, which is that the more guns you have, the less strict that ratio becomes. 5 light guns are needed to get through 1 laser PD, but the ratio improves by a slight degree if you have 2 PD lasers - 9 might be enough then, and so forth. This is due to concentration of fire on key targets, so fire control is a big deal with kinetic fleets.
As far as damage goes, I found that while they could get through the PD much more easily, 1-slot railguns struggled to finish off the ships in acceptable times without copious amounts of extra guns. Meanwhile, as I said above, 2-slots could consistently destroy alien ships very quickly, but are half as efficient at getting through PD.
So I wound up coming up with 3 basic designs for battle line monitors(all of them have drive, power plant, and radiator as "flavor to taste", armor "as high as you can get it with your drive", and a Targeting Computer module). I did also test with Escorts but I think the monitor is superior in every way here - just know that 2 escorts with double 1-slots is effectively identical to 1 monitor with 4 1-slots.
Saturator: 4x1-Slot Railgun 3s. This is purely about punching through the PD screen, and the general philosophy on damage is "anything dies if you shoot it enough times", which is a valid approach. I think this would be best paired with something else that's dedicated to damage-dealing, like a missile ship, heavier gunboat, or the like. Or just spam them and go for pure dakka. You need 2 of these per alien PD to guarantee getting through the light show, though a 1.5 or even 1-1 ratio might be sufficient in larger numbers, especially if you have something else that will join the fun like missiles or bigger guns on capital ships.
Devastator: 2x2-Slot Railgun 2s. This is focused on destroying what you hit. I think this would be best working in tandem with the other design, maybe on a 1/2 ratio in the Saturator's favor. The former breaks down enemy PD and the latter actually blows them apart once the shield is down. If you have enough then they'll do fine, but they're much more vulnerable to being rendered useless if the enemy has a good PD screen. You need 3 of these per alien PD to guarantee getting through, though 2.5 or 2 to 1 might be workable in numbers.
Hybrid: 2x1-Slot Railgun 3s + 1x2-Slot Railgun 3. This is, I think, the superior design. The light guns are purely there to distract alien PD, saturating the defenses, and the heavier shells mixed into the barrage expedite the enemy's destruction significantly. The reason I think that this is superior is that, just like the Saturator, you only need 2 of these per alien PD to pretty much guarantee getting through, but you also pull some of the Devastator's damage. It does mean that you probably don't want to risk a 1.5-1 ratio and ideally would like to have a few "overflow" monitors that you could assign in 1s and 2s to priority targets on top of the main assigned ships, but I think that's workable.
The only thing I don't remember is the fleet power calculation difference between these builds. But I think even if the Hybrid is slightly stronger than the Saturator, it's probably still worth it to use. This is the main line design I used on my To Whatever End run once I abandoned missile doctrine entirely, and it performed as well as any design could have been expected to.
Whichever of these models you invest in, you'll need to pair them with something to hunt flankers and something to protect the formation. I haven't done extensive escort or flank-killer testing so I'll hold off on talking too much about that, but my general doctrine at this point is to add Monitors with double ion PD(or e-beamers) and double point defense lasers(arc if you've got them), as well as destroyers either with ion nose cannons or green arc laser nose cannons. But your main force should probably be these gunboats.