Really slow 802.11s throughput between a QCA9880 and MT7612 device (5Ghz) in one direction

Hi,

I am trying to set up a WPA3 mesh link between these devices. but the throughput between my Devolo 1750e and Xiaomi mir3g is really bad in one direction using 5Ghz wifi.
Unfortunately I don't have another wifi 5Ghz router to test if the devolo or the Xiaomi is the cause but I have read a QCA9880 NIC works well with a Intel NIC in mesh mode, so I suppose the cause lays in the mt76 driver.
The throughout results are using the mt76 driver @bf60f43b12fb14d2acff2c6608e37645c3ee4242 but the driver in the current OpenWRT trunk behaved the same. The Devolo device is using the mainline ath10k driver and firmware.
Can I collect some useful data for you?

root@OpenWrt-Xiaomi:~# batctl tp $(mac of devolo)
Test duration 10236ms.
Sent 28640304 Bytes.
Throughput: 2.67 MB/s (22.38 Mbps)
root@OpenWrt-Xiaomi:~# batctl tp $(mac of devolo)
Test duration 10280ms.
Sent 39606984 Bytes.
Throughput: 3.67 MB/s (30.82 Mbps)

root@OpenWrt-devolo:~# batctl tp $(mac of Xiaomi)
Test duration 10164ms.
Sent 19188 Bytes.
Throughput: 1.84 KB/s (15.10 Kbps)
root@OpenWrt-devolo:~# batctl tp $(mac of Xiaomi)
Test duration 10268ms.
Sent 13284 Bytes.
Throughput: 1.26 KB/s (10.34 Kbps)

Thank you and the team for the great work for the mt76 driver!

Start by reproducing the directional throughput measurements with batctl tp between the QCA9880 and MT7612 devices, using the mt76 revision bf60f43b12fb14d2acff2c6608e37645c3ee4242 and the current OpenWrt trunk. Compare the mt76 and ath10k driver behavior and collect the useful diagnostic data requested in the issue. Done means identifying a reproducible driver cause or documenting the evidence needed to isolate it.