Is my university using TA's excessively?
Actually, I don't think it is excessive, though it may be a bit steep. It was a long time ago, but when I was a PhD student in mathematics at an R1 in the US, the &quot;load&quot; of a TA was about half that of the teaching load of a professor (1 course equivalent vs 2 for a professor). I don't see anything in your list that is really out of bounds, assuming #1 is occasional. In fact, all of it is good training for anyone wanting a career in academia. You need to practice all these things to get good at them.
I was thrilled (thrilled, I say) when, as an advanced TA, I was given complete responsibility for one section (of many) of an elementary course. The course was pretty standard so there wasn't much course design prep and the final exam was common to all sections, but, otherwise, the course was mine.