оттуда же: MikroTik´s old driver is completely made by MikroTik itself. There won´t be any MU-MIMO, no WPA3, no 802.11k/v/r, nothing what you´ll see with "WiFiWave2"
"WiFiWave2" is based completely on chipset vendor´s oem driver. "WiFiWave2" package contains multiple kernel modules and firmware files. Therefore it is so big. MikroTik could easily create a smaller package e.g. for IPQ4019 (cAP ac, hAP ac2,...) so it can be installed on their ROM. Of course 128MB of RAM is sufficient. But MikroTik doesn´t seem to want us to have proper wireless support on their old devices. They earn money by selling cheap hardware not by selling software or support contracts.