Su-76. 10.6 tons. 35mm frontal armor. Modified T-70 chassis.
Marder II and Wespe. 10.8 tons. 35mm frontal armor. Modified Panzer II chassis.
Marder III and Grille. about 11 tons depending on variant. 50mm frontal armor. Modified Pz-38(t) chassis.
.....On paper they look like three peas from the same pod. However I'll hazard a guess the German built vehicles were more reliable and had superior crew ergonomics.
15 ton Jagdpanzer 38(t) based vehicles produced during 1944 to 1945 were superior in every way. And they ought to be as they were a generation newer and produced from a clean sheet of paper rather then jury rigging an existing light tank chassis.
Also, it should be said that the German counter parts continued to have a viable AT function for most of the war, while the SU-76 really only had that ability earlier in the war, or if lighter vehicles stumbled into its range.
6 ton Sd.Kfz.250/8 light APC with 7.5cm HEAT rounds probably had more AT capability then Su-76. However it wouldn't be my first choice for an anti-tank weapon. Employing such weapons against medium tanks is an act of desperation.
No, the 76mm on the SU-76 was weaker than the German 75mm tank guns (Except the 75mm/L24). But it was enough to deal with medium tanks like the Pz III and PZ IV. The German 75mm model 40 was more in the league of the Russian 85mm. The Russian 76mm was more in the league of the US 75mm M3.
I thought so at one time, but they both used the same ammo which had the same performance. Tests of the ZiS-3 were probably using a later war improved BR-350B round. Tests of the F-34/ZiS-5 were probably of an earlier round. So what was being compared was the ammo not the gun. The ammo improved a tad not so much the gun.