Look at it this way: shooters fire 5 to 15 times per second (.96 Gal -> Aerospray), while Dynamo doesn't even get 1 full swing per second. The worst rng set for a shooter is 40% chance to shoot outside the center reticle while on land and that's not even accounting for the first few shots having almost no rng for most (all?) of them. In 1 second, it's extremely unlikely that a shooter won't kill a continuously well-aimed-at target, let alone do no damage whatsoever.
While rng is certainly a disadvantage in combat for shooters, it's nothing compared to what Dynamo goes through. In that same 1 second, it's likely that Dynamo might do no damage whatsoever based purely on rng. Hell, it can go multiple seconds like that, even with multiple targets in range. Then when you add the weapon's incredibly poor ink efficiency to the mix... It makes for a weapon with incredible weaknesses, and incredibly inconsistent reward.
Dynamo's just in such a sad state and since years Nintendo keeps refusing to actually fix the problem.