A couple of "long shot" suggestions if you try the ath10k-ct driver/firmware again. For the record, I've yet to observe a change in my r7500v2 wifi behavior when playing with these features...
In your testing with ath10k-ct with apple devices, did you try disabling mu-mimo on the r7800? (The method I used to disable mu-mimo is here.) Alternatively, do you know if the apple (or other) devices are mu-mimo capable and if so, is mu-mimo being used with any AP/firmware?
Also, I noticed hostapd advertised vht capabilities are inconsistent with those reported by iw phy (which I think are obtained from the ath10k-ct driver/firmware - I'm not 100% certain). I made an attempt to adjust the 5GHz hostapd config file to "correct" this but I do not observe a difference - at least the way I did it. See here for details about trying that - the r7800 may be different.
HTH