Makes no logical sense, Wiggins and Thomas simply continued what we already knew was possible from the track with Merckx, Hinault, Indurain, Coppi, Bartali, Anquetil etc all being world class endurance track racers, hour record holders, timetrialists etc. All that really separates their background is there was no real pathway to pay your bills and race the road in the UK and largely no real access into continental racing without essentially becoming Italian, French or Spanish like Simpson or arguably Kelly and Roche.
End of the day, it's the same 2 muscles in your legs, the same two lungs and the same capacity to move oxygen and clear lactate that decides who is fastest uphill. Track racing is about as pure as endurance gets because it doesn't even have variables, like getting a break, moving abroad, crashing, luck, not being a certain nationality etc, you are either very well suited to endurance racing on the track or you are not and are a track sprinter if you have those capacities.
I'd agree, the reason Thomas bridges the gap is for 3-4 month a year he has the mental ability to really sacrifice lifestyle in order to bridge to GC racing weight, a rider like Gaana or probably won't. Tarling, maybe, but those natural TT and pursuit weight requires way more sacrifice than your Pogacar, Froomes or Vingegards.