Some questions to JAZZCNC or any other closed loop stepper experts

[m_c]

Correct me if I am wrong, but don't say that I "happy to redefine terminology", because I am not. I did not make any calculations before, but definitely not redefined anything and torque is definitely increasing when you add a reduction gear. I think you understand that very well, but if you don't understand what I am saying that's a different thing, and is perfectly possible that I am not that clear, but that does not justify such statement. I am not stupid, I can read charts, make calculations (in ANY sort of units) and so on. You are not the only one with engineering background and long and prosperous career.

Erm..you did though -

I think the only difference between AC and DC servo is that an AC servo driver has the rectifier built into the driver, while a DC servo must be fed using an external DC PSU with a rectifier circuit in the PSU. When I say DC servo, I mean just that the driver needs DC current, but it is still a servo, and NOT a closed loop stepper.

How any given motor controller gets powered, does not define the type of motor attached to said controller.
An AC motor doesn't suddenly become a DC motor because the controller needs DC power.