Ok already some answers in this forum.
-priority marking is not done by WMM itself. DSCP is not used by WMM. So WMM needs the mangle rules to have the priority set. (from: http://forum.mikrotik.com/t/why-isnt-wmm-support-default/111827/1)
-setting priority via mangle rules can require a long list of rules, and many queues. QoS has to be configured by specifying those priorities. (from: http://forum.mikrotik.com/t/using-routeros-to-qos-your-network-2020-edition/66683/1)
-The relation to A-PMDU is clear in the priorities from the mangle rules, but its implementation is not known. How many A-MSDU/MSDU packets in one A-PMDU? Fixed? Variable? Value per priority ?
The priority setting of WMM looks very similar to the “nv2-queue=4” in the nv2 frame priority. … https://mum.mikrotik.com/presentations/KE18/presentation_5035_1517536100.pdf