Thank you for sharing your findings - glad you could bring this little device back to life!
On a sidenote: while testing last month I managed to get an throughput uplift with the iPhone11 test at 5Ghz@80Mhz from 348 to 829 Mbits/sec
see EAP615-Wall; OpenWrt or Stock? - #11 by ed8
background:
Mar '23 I tested 80Mhz with two active access points on channel 36 and 48
Dec '23 I tested 80Mhz with one active access point on channel 36
=> i think that the second test was able to use a higher modulation level like HE-MCS 10 because channels did not overlap like in the first test (I did not pay attention to this though so am not 100% sure; it might also be that the snapshot version has improved since then).