The .52 Gal is something I feel could be S Rank. It has high power (a bit of Damage Up is still a good investment tho), solid range and decent mobility, as well as Splash Walls for defense and blocking off areas (even after the nerf, I still think it's quite good) and Killer Wails to deny enemies access to a space for a few seconds. The only real problems are that its range is beaten by quite a few other shooters and its fire rate isn't as fast as most guns (at least, it doesn't feel like it is when I use it), but those I feel are compensated for by its strengths.
Dual Squelcher may or may not be S material. Its range is great, its fire rate is fairly fast, its spread is fairly narrow, Splat Bombs are good for hitting areas you can't quite reach, and Echolocator is still great, but the Dual Squelcher can probably build it faster than the E-Liter 3K. However, the power per shot is fairly low, and its mobility while firing, though faster than it used to be, is still a bit slowish. Honestly, the only thing holding me back from saying that this is S rank is that I don't see it all too often online, or don't notice it if I do, but I'm not sure if that's enough to disqualify a weapon from S if it fits your other requirements, which I feel the DS does.
I used to fear and loathe the Dynamo Roller. 90% of the time, when I saw one, it dominated me for the entire match. As for the Dynamo itself, its strength is superb and its reach is also pretty good. Sprinklers are a good way to cover areas remotely so you can go swing your Roller at enemies as well as charge Echolocator, which is still amazing. The speed on the Dynamo's swings is an issue though: I said 90% of Dynamos wrecked me, but the oher 10% were people I got the drop on and splatted before they could get a swing off, so slowness is definitely a problem with this weapon. Additionally, patch 2.2.0 nerfed the Dynamo (and its golden variant) quite a bit in a few ways (you can't kill with hits that extend beyond the Roller's width, I believe, repeated flicks don't fling as much ink, and I think its ink cost went up or the time before you can refill your ink tank increased, but I'm not sure which of those happened), making it less of a presence than it was. Before, I would have put the Dynamo in S or A+ with little hesitation; now, it's solidly A+, but I feel it slipped out of S rank.
The Forge Splattershot Pro... *sigh*. Its range, power and speed are all pretty good, and its spread isn't too wide (or at least it doesn't feel that way when I'm using it), and its ink efficiency just got better after the latest patch. Point Sensor is a good, cheap way to check for enemies in ink and get a brief Echolocator effect on enemies, and while Inkzooka has been slowed a bit it's still very good. However, you don't really have much of a way to deal with enemies behind cover beyond hitting them with mini-Echo, which can be a bit of a problem, and while I don't feel Inkzooka's recent nerf hits the ForgePro as hard as the Tentatek, I still feel the ForgePro suffers as a result. The ForgePro's still a damn good weapon, and I could see a case for it remaining in A+. I guess my main problem with it is that I look at it and think "I just can't see this being that much better than the regular Pro any more."
Custom Jet Squelcher I agree with. Its range is quite long, its power is respectable, and its fire rate is alright (not Dual Squelcher, but not .96 Gal either). Burst Bombs are decent for hitting around cover, and while I haven't had much success with it, I would suppose that you could throw one at an enemy to soften them up and then finish them off with your main shot. Kraken is still a great defensive tool despite taking more nerfs. The Custom Jet Squelcher's mobility while firing is crap, but that's not really why you'd pick a Jet Squelcher, so it's not really a big deal. I could honestly see this being S rank, but A+ is fine too on this one.
The Krak-On Splat Roller is quite good. Its power is great (I know it got nerfed a bit so it couldn't splat with shots beyond the Roller's width, but I never really noticed this because all the Krak-Ons I faced had good aim), its speed is okay, its turf-covering ability is very good, and its loadout makes it an effective support weapon. Well-placed Squid Beakons can allow teammates to return to fights faster than they normally would and from places that could normally be safely ignored (and can also be used as a second-rate Splash Wall if it has to, though I wouldn't recommend relying on this), and the Kraken is a good way to escape from bad situations or get a quick surprise splat (though it's not so good for offense any more). Its range is kinda crap, and Kraken isn't the offensive force it used to be, but the Krak-On is still quite good. Not sure it's quite in A+, I'd put it in A myself, but A+ works too.
The Splatterscope is a pretty good Charger, with a decent charge time and not-E-Liter-but-still-great range, and the standard one-shotting ability of Chargers. Additionally, Splat Bombs provide the ability to attack enemies behind cover or areas you can't easily snipe, or roll one to quickly attack a nearby foe. Splat Bomb Rush lets you pressure areas and just prevent enemies from accessing places with bombs for a bit. If you don't need Echolocator or the extra range that an E-Liter provides, the Splatterscope is a solid choice. A+ is a good place for this weapon.