Using one damage up main and one sub counters any amount of defense up, ensuring a four shot splat with it. Using around a main or five subs of defense turns the tentatek into a four shot kill, makes the 52 gal a three shot kill, and may increase your survivabilty against blasters if they don't hit you directly enough, and forces snipers to charge their shots more to splat you. Using damage up and defense up causes the dual squelcher to counter all of those weapons (the ones I listed at the beginning and more) with ease.
I have quite a few problems with this section. Let me list them:
1. Not many people actually run more than around 2 mains and 4 subs of Defense Up. You might benefit from having a sub or two of Damage Up, but do you really need to ensure a 4HKO against absolutely any amount? I'll admit that I'm no Dual Squelcher main, but foregoing mainstays like Swim Speed Up for the sake of countering perhaps 1 player in the world who runs 3 mains and 9 subs of Defense Up seems a bit excessive.
2. Just 1 main and a couple subs of Defense Up is not enough to reliably allow you to survive an extra hit. .52 Gals in particular usually run significant amounts of Damage Up, so such a middling amount of Defense Up just isn't going to cut it against them. Some Tentateks also run enough Damage Up (it only takes 3 subs) to counter that amount of Defense Up, and Blasters (apart from the Rapid family) are still going to 2HKO you most of the time.
3. The Dual Squelcher isn't the only weapon that can make good use of Defense Up. In particular, the .96 Deco can do so to a greater degree because it never has to worry about the enemy's Defense Up turning it into a 3HKO.
There is one exception however, the 96 gal. If you look at the weapons stats however, the dual squelcher has very very slightly more range than it.
There is no difference in their ranges. It only feels like there's a difference because of the .96's infamously poor accuracy, which makes it harder to hit distant targets with it. However, this is counterbalanced by the fact that if you are attacking someone who is just beyond your effective range, the .96's falling shots retain their 2HKO power better than the Dual Squelcher's shots retain their 4HKO power. (Thus, if neither weapon misses due to RNG, the .96 actually will fare better at the very outside of its range than the Dual Squelcher.)
It also has splat bombs which can take out walls with ease.
Bombs do not instantly solve all your problems when an enemy deploys a Splash Wall. The wall will still offer a brief moment of protection, and you and the enemy will expend roughly equal amounts of ink throwing the bomb and the wall. Thus, unless the enemy is stupid enough to walk in front of the wall and get killed by your bomb, you'll only manage to more or less reset the playing field by bombing the Splash Wall (which is to say that the .96 will still have the advantage due to quicker kill time). Also, bear in mind that the Tentatek still struggles against the .96 Deco despite being able to bomb Splash Walls.
Ultimately, the Dual Squelcher isn't a bad weapon. It's just not as easy to fit into a team composition as mainstays like the .96 Deco and Tentatek. The Dual Squelcher's relatively poor killing power means it is at a disadvantage against many other shooters (NOT the other way around), and since its range is less than that of the Jet Squelcher, it isn't completely safe when engaging Tentateks and .52's. It's certainly a solid weapon, but OP? Definitely not.