I really wouldn't know the answer to your questions without knowing more about the drivers you are using. However, the peak current is what the motor can tolerate without magnetic saturation, whereas the RMS current is what causes the electrical heating , which is almost entirely due to resistive losses in the copper windings.

To complicate matters, the "better"(?) drivers reduce the driving current after a short period, once the motor has hopefully reached its target. This allows high movement torque but reduced steady state heating. And if you go further ie closed loop steppers, the control scheme is more sophisticated so that the motor current is a more direct function of the applied torque ie no more than it actually needs to be.

Leadshine are a solid outfit, so in the event of conflicting information, I'd go with what they say, not least if you are using their drivers. I expect there are application notes by Leadshine explaining not just how to set up their drives but possibly even giving some insight into what the settings do and mean. I've used their closed loop steppers in the past and was quite impressed with the level of documentation provided.