As an "ex faults agent", shouldn't you be much more able to investigate and solve your own problems yourself than most people on the forums?
You haven't given us any details of the VDSL2 connection stats, or your estimated speeds, so there's nothing there for us to look at. Now you've mentioned wifi, but presumably you would have already checked with a wired Ethernet connection to determine if it's a problem with the wifi or something else.
You could try doing some ping tests to check for packet loss, I'd do some pings with larger packets, because the default ping packet size being much smaller than data carrying packets can make the results unrepresentative of a problem affecting data transfer.
However, I wouldn't expect something affecting the VDSL2 connection between you and the cabinet to only affect specific websites. You could try using different DNS servers if you haven't already tried that, although I wouldn't expect it to make much difference.
I don't find wireshark an awful program. I generally start it capturing everything, then do whatever it is I want to investigate, then examine the captured packets. Everything using https these days can limit what wireshark can decode.
