Thanks Scott!
For me it’s actually the opposite: doing the circuit takes much longer than one-two at a time because of the cognitive load of keeping track of what I’m doing, what I have done and what I have left to do. I think it’s a kind of mental laziness: for all other training I do (running, walking uphill, etc) my brain can be completely zoned out, whereas doing the strength circuits I actually have to pay attention and focus otherwise I start to forget exercises.
I think I will continue with doing one at a time for a few more weeks and see if it starts to feel too easy (that is, point 2 in the original post becomes a problem).