Considering Jaffa weapons have an aimed range of 100m, the P-90 actually IS a weapon of war in comparison.
As the picrel Matok staff weapon heats it actually becomes less accurate. According to line of sight positions, Teal'c aimed at Sha're's neck yet hit her lower chest, and this is only 10m away from her, due to heat after a firefight.
Zatnikatels actually have as much native accuracy as Taklukhnatagamuntoron, far more than Matok's, but because Zatnikatels are a handheld weapon there's no way to aim it at any distance.
Also they don't have much in the way of armor defeat capability. Their best anti armor weapon is the staff weapon, which on impact produces a HESH warhead effect on the target, and also lights nearby flammable stuff on fire. This makes it ok at penetrating rolled homogenous armor, and at killing humans (its like getting hit by a flaming sledgehammer), but really bad at penetrating armor designed for it.
If they got an Abrams tank through the gate, staff weapons would have no effect on it. Even powerful glider weapons would fall short of the energy needed to defeat it… only a lucky hit from an Al'Kesh would knock out an M1 Abrams tank.
The benefit of Goa'ould weaponry comes from the fact that they will work for thousands of years, and that they're scary. This is very useful for a nigh-immortal race of power tripping psychopaths, but even in comparison to Tauri civilian weapons…. they are not weapons of war.