And now... I'm completely and totally confused. I installed iperf3 on router and macbook, run router as server, and connect via client:

MacBook-Pro % iperf3 -c 192.168.8.1 --bidir
Connecting to host 192.168.8.1, port 5201
[  5] local 192.168.8.200 port 52905 connected to 192.168.8.1 port 5201
[  7] local 192.168.8.200 port 52906 connected to 192.168.8.1 port 5201
[ ID][Role] Interval           Transfer     Bitrate
[  5][TX-C]   0.00-1.01   sec  55.0 MBytes   459 Mbits/sec                  
[  7][RX-C]   0.00-1.01   sec  37.1 MBytes   310 Mbits/sec                  
[  5][TX-C]   1.01-2.01   sec  35.8 MBytes   300 Mbits/sec                  
[  7][RX-C]   1.01-2.01   sec  54.0 MBytes   453 Mbits/sec                  
[  5][TX-C]   2.01-3.01   sec  36.2 MBytes   304 Mbits/sec                  
[  7][RX-C]   2.01-3.01   sec  59.5 MBytes   499 Mbits/sec                  
[  5][TX-C]   3.01-4.00   sec  35.4 MBytes   298 Mbits/sec                  
[  7][RX-C]   3.01-4.00   sec  56.2 MBytes   474 Mbits/sec                  
[  5][TX-C]   4.00-5.00   sec  37.0 MBytes   310 Mbits/sec                  
[  7][RX-C]   4.00-5.00   sec  54.2 MBytes   455 Mbits/sec                  
[  5][TX-C]   5.00-6.00   sec  35.9 MBytes   300 Mbits/sec                  
[  7][RX-C]   5.00-6.00   sec  54.0 MBytes   452 Mbits/sec                  
[  5][TX-C]   6.00-7.00   sec  39.4 MBytes   331 Mbits/sec                  
[  7][RX-C]   6.00-7.00   sec  59.4 MBytes   500 Mbits/sec                  
[  5][TX-C]   7.00-8.00   sec  37.1 MBytes   311 Mbits/sec                  
[  7][RX-C]   7.00-8.00   sec  57.5 MBytes   481 Mbits/sec                  
[  5][TX-C]   8.00-9.00   sec  36.9 MBytes   309 Mbits/sec                  
[  7][RX-C]   8.00-9.00   sec  55.1 MBytes   462 Mbits/sec                  
[  5][TX-C]   9.00-10.00  sec  37.6 MBytes   315 Mbits/sec                  
[  7][RX-C]   9.00-10.00  sec  57.8 MBytes   484 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID][Role] Interval           Transfer     Bitrate         Retr
[  5][TX-C]   0.00-10.00  sec   386 MBytes   324 Mbits/sec                  sender
[  5][TX-C]   0.00-10.03  sec   384 MBytes   321 Mbits/sec                  receiver
[  7][RX-C]   0.00-10.00  sec   548 MBytes   460 Mbits/sec    0             sender
[  7][RX-C]   0.00-10.03  sec   545 MBytes   456 Mbits/sec                  receiver

iperf Done.

So... now its bouncing around, where ookla speedtest shows consistent 2x Tx vs Rx, this shows mostly Rx faster (but not the first round)...
I haven't had coffee this morning - what am I missing here? Is it possible internet and only internet traffic downloads more slowly only when connected via wifi?

(edited to show bidir and because my first try I actually had an ethernet cable connected)