I am not sure why this is so staggering anymore. The best triathletes in the world are seriously good runners. Maybe not quite world class but definitely top end national standard whilst also being great swimmers and cyclists.
Alex Yee is one of the best runners in triathlon and is only 23. He regularly runs high level road and track times in legit road races:
https://www.thepowerof10.info/athletes/profile.aspx?athleteid=663344
He recently ran 13:26 for a road 5k and was only 6 seconds behind Marc Scott who ran a British record. Yee's time was also inside the old record so he is now second on British all-time list for a road 5k.
Also, didn't a US triathlete recently beat some of the best US guys in that road half marathon? I know it may burst a few egos but the worlds best triathletes are pretty much equal with the best runners outside of East Africa.