Hey Adam,
please correct me if I’m wrong, but I think the stepper motor of a rotary axis is much less demanded than those of the XYZ axes. Mostly it does not even rotate (in the examples linked here), which means it is all current just for the holding torque. The question is whether you request the rated power at all. As long you don’t plan to use it as a lathe.
Don’t you have an ammeter? There are also inductive consisting of a pair of pliers and do not require electrical contact.