For testing purposes I reinstalled factory firmware on my Cudy WR3000 MT7981 RFB/R31 device running Kernel 5.4.219. While it seemingly lost all Short GI capabilities since installing OpenWrt, the OpenWrt-based factory firmware with customized LuCI is just doing fine with HE160 (AP and mesh point) on both channels 36-64 and 100-128.
Power levels look much higher as well, it's transmitting with the allowed ETSI levels instead of just 400 mW, outperforming my Archer C7.