On the subject of "thunder rods’, I did a bunch of math on that for the Lost Thread, but essentially, you can turn it into a cluster munition with ease, sleeting down several hundred projectiles, each with the same or more KE of a 120mm APDSFS penetrator, as currently fired by the Rhienmettal gun on the M-1A1. In short, they could be made into absolutly lethal killers.
It’s just much easier and cheaper to do it from inside the atmosphere.