RMC, GSIs are part of life at any major research university, whether it is Michigan or Penn or Harvard etc…
That being said, at a top department like Michigan’s Political Science department, GSIs are as knowledgeable about undergraduate courses as professors. They are usually 3rd or 4th year PHD students who graduated from college with near 4.0 GPAs and really know their stuff. GSIs will usually not be involved in advanced classes, only in larger, intro-level classes.