@Michal-Rok thanks for the feedback, sorry it got you no further either.
Yep, I disabled the firewall entirely, even as far as removing the rc startup link and rebooting with no change. iptables -L shows nothing at all at this point (what you'd expect really). I tried forcing the wlan interface into the bridge (br-wlan) also with no change at all. I disabled dnsmasq and forced the resolution to Google (18.104.22.168) with, of course, no change either (which you'd expect as nothing appears to arrive on the router itself).
Was there a reference anywhere to what the "option mode '9'" (or 'sta') does and any other options relating to this area of the config? I searched on anything WRT but didn't show anything about the ralink unit so was rather roadblocked at that point.
One other point that I noted was that I needed to ensure my channel was low in order to work at all, almost like the AU flag wasn't being used. Not a huge deal as a quick scan on the MT suggested 6 was the best channel for me but changing from AU to US and/or back didn't seem to change anything at all.
As far as running with no security, I might try that trick and see if I can get any ideas of what is happening.
I originally tried connecting to my mobiles hotspot to get running and that worked, then modified the config to suite the MT, hoping that the initial config was doing something more when it was first coming online but as mentioned by a few others, that made no difference either.
Frustration to say the least.
Has anybody had any luck with a USB wifi adaptor and an MT on these units?
I love my MT(s, I have a few running in the house) so a decision to swap them isn't going to fly and I'd rather just accept that the Omega isn't for me than contemplate the alternative.