If anyone is interested in comparing what "features" each wifi firmware provides, I sampled a few, as reported by
dmesg | grep 'firmware ver'
Mainline/old:
firmware ver 10.4-3.9.0.2-00131 api 5 features no-p2p,mfp,peer-flow-ctrl,btcoex-param,allows-mesh-bcast,no-ps,peer-fixed-rate crc32 23bd9e43
firmware ver 10.4-3.9.0.2-00139 api 5 features no-p2p,mfp,peer-flow-ctrl,btcoex-param,allows-mesh-bcast,no-ps,peer-fixed-rate,bit22 crc32 84f36f58
firmware ver 10.4-3.10-00047 api 5 features no-p2p,mfp,peer-flow-ctrl,btcoex-param,allows-mesh-bcast,no-ps crc32 19ca6df2
CT:
firmware ver 10.4b-ct-9984-fW-13-5ae337bb1 api 5 features mfp,peer-flow-ctrl,txstatus-noack,wmi-10.x-CT,ratemask-CT,regdump-CT,txrate-CT,flush-all-CT,pingpong-CT,ch-regs-CT,nop-CT,set-special-CT,tx-rc-CT,cust-stats-CT,txrate2-CT,beacon-cb-CT,wmi-block-ack-CT,wmi-bcn-rc-CT crc32 7ea63dc5
I also ran some iperf3 tests, one side is a wired Linux server, the other side is a 2019 MacBook Pro (5GHz radio). Same build (master-r15759-ce4cb8e51d-20210214), same location, the only change is the firmware:
Mainline/old firmware 10.4-3.9.0.2-00139:
[ ID] Interval Transfer Bitrate Retr
[ 7] 0.00-10.01 sec 571 MBytes 478 Mbits/sec 110 sender
[ 7] 0.00-10.00 sec 568 MBytes 476 Mbits/sec receiver
CT:
[ ID] Interval Transfer Bitrate Retr
[ 7] 0.00-10.00 sec 205 MBytes 172 Mbits/sec 250 sender
[ 7] 0.00-10.00 sec 202 MBytes 170 Mbits/sec receiver
Stability, performance, mainline looks by far much better for me than CT.
FWIW, similar reports here: https://github.com/greearb/ath10k-ct/issues/138