Low end drives with cheap slow optocouplers can't handle 400kHz, not even 200kHz and often not even 100kHz.
Usually chinese drive manufacturers put slow optocouplers into the drives, because they are cheap and it does matter if they put a $0.5 optocoupler or a $0.05 optocoupler when they make 100 000 drives a year. Then that is a big difference in cost and in their profit.
And in most drives it does not matter much if you use medium to very high resolution and stepper motors can't rotate very fast, because on high speed they loose torque and so using slow optocouplers is kind of understandable.
Mostly servo drives can handle 400kHz, because servos can have high encoder resolution and therefor using fast optocouplers is an advantage or maybe I can say it is a requirement.