>The problem with conventional non-guided or unaided rocket artillery or ground to ground rocketry is that it's extremely inaccurate, even by conventional artillery standards which can have a probable error of several hundred meters.
What the fuck are you smoking? The only way you could think that is if you're looking at maximum obscene ranges of 200km+ and comparing that with a piece used in its intended effective range.
For regular artillery to have a CEP of several HUNDRED meters is if its a self propelled piece gunning it through forest, Tokyo drifting into position, firing immediately a RAP at maximum range in a tornado.
A truck mounted artillery which is in a prepared position and takes the time to set up the jacks, takes meteorology into account, zeros in a shot, and fires within the 5-20km range common for artillery, can have a CEP of 50m easily. That's simple dumb artillery round fired from a well prepared position.
In comparison MLRS which usually has a cheapo laser gyro guidance chip, and has air brakes or fins to center it, has a CEP of around 15-30m. Rockets can also fit simple radars in their nose for terrain matching, like the Iskander, and have pinpoint accuracy that exceeds GPS at similar cost.
Jamworthy satellite guidance not required.
Also you have to take yield into account. For example the cheapest longest range modern missile is a type of thin/packable Scud invented by Serbs, it has a range of about 300km and a truck can carry up to 12x pack of them. It's maximum range accuracy is 150m in the worst case scenario, well short of your "hundreds of meters" but still bad right? Wrong. Given that this circle is being filled with 5000lb of explosive, it doesn't fucking matter.