It's a frickin beast, and i agree with the specialists, it doesn't work well... in fact, you can directly oppose Hydra Splatling users with Heavy. Though, i'll argue that the range is a massive help if your playing defense. (And actually, you can actually ambush any of the splatlings with an actual gun. Take note, i said ambush, you can't take Splatling'ers on directly.)
Actually, overall, i'd say that if you plan on sitting on your butt the entire match, use Hydra. If you plan on adjusting to whatever happens, Heavy. If you actually plan on being active, (i'm not sure on this, i tried light once and nope'd it) Light.
But that's just the impression i get with the splatlings, i might be using them wrong, and this is not taking specials into play.