Ah, you meant the Tentatek? That changes things?
You still have the rapid-fire superiority, but now you have a more balanced weapon in the Tentatek. Suction Bombs help make enemies move and can be placed to catch enemies by surprise to splat them (at least it feels that way, might just be me walking into their range without noticing, or maybe just lag), and Inkzooka has amazing range (just short of E-Liter range, with no charge time, and also it shoots really tall inknados) and power (a one-shot. Always). That on top of the rapid-fire for close combat.
On the other hand, the Slosher wins at mid-range unless you whip out the Inkzooka, can ink turf better since its splashes don't have holes (for what I mean, if you fire the Splattershot for a seconds, there'll be tiny areas where ink didn't land, so that turf wasn't covered even though it's in your range: Sloshers, Rollers (while rolling) and I think Chargers don't have this problem) and Burst Bombs are faster than splashing (or at least it feels faster) and can be thrown at faraway enemies (though you'll need a few hits unless you get center-shots on all of them), and Inkstrikes are still quite useful.
So overall, it depends on what you need. Tentatek is a great combat-focused weapon, while the Slosher is best for midrange combat and inking turf.
Well, actually, some of those do have weaknesses, though not big ones. For example, the Splattershot Pro requires quite a bit of investment into Ink Savers/Recovery Ups because its ink efficiency is quite bad, the Tentatek can't really deal with long-range enemies outside of throwing Suction Bombs at them unless you have Inkzooka ready to go, Forge Pro combines the poor ink efficiency of the Splattershot Pro (though only on the main weapon this time) with the Tentatek's inability to deal with long-range enemies well without Inkzooka (except worse, since Point Sensors don't actually deal damage), Splash-O-Matic has short range, Dynamo Roller is slow, E-Liter needs a Damage Up or two for Burst Bombs to do well at close range. Still, those are hardly crippling weaknesses (even the Forge Pro, which I feel is inferior to the regular Pro, is a great weapon since it's good for team-support with the Point Sensors to locate enemies for your team and Inkzooka to crush faraway foes who would otherwise give your team trouble), and they're all very good.
Also, does Marie actually do that? Where, exactly?