@e4d yeah.... it's not the total torque that changes, it's the torque per step. So simplified you got two coils and we are looking at two teeth on the rotor. Coil A is at full current so it's pulling the full torque into that position on tooth A which is a full step position. A half step will put half current on each coil so you only have half the torque pulling into the middle of the two teeth. Continue to put full current on coil B, and zero on coil A and you get full torque to move you from the mid position between Teeth A and B to the full step position of B.
Whether you microstep or not you go through full current on a coil in the full step positions so your total torque is the same over a distance, but how well you constantly and repetively hit a microstep outside that full step position decreases as you increase the number of positions between full steps. TLDR; the tiny changes in current may not actually move you that tiny amount between the teeth, but when it comes to the tooth being fully lined up it's all the same.