As I said the argument can be made that in the allied camp there was a larger difference between tank destroyers and actual self propelled artillery, however in the German and Soviet camps, SP arty was actually an assault gun which was as capable, if not more so than the "tank" destroyers and taking out armor and that is in addition to maintaining their role as an infantry support weapon.
Quite true. I had read that the German Army was so concerned about inflated kill claims by assault gun battalions that some Gestapo Officers were repeatedly sent to investigate. What they found was that the artillerymen of the assault gun units were actually much more competent at killing Russian tanks than the armored AT units.
It was a simple matter of the German artillery direct fire method which called for one shot purposefully long, one short, then one on target-it worked well. The PZJ crews were instructed as tank crews and attempted first round/first shot hits. The artillery method was more accurate-in those days.
IIRC, tank busting guns were the majority type given to assault gun Bn's from 1943 on. There were still perhaps 1/3 (of each Bn) equipped with cheaper guns made to fire HE shell.