That's what I was thinking. Since the HDMI capture shouldn't effect the image/grade ...It looks like his picture profile (Canon LUT) on the Canon camera is hurting the image.
What bugs me is once the lighting was in place, he didn't try to manually expose the webcam to see how good it could actually be with just a "modest" lighting upgrade. 2x Key Light Airs comes to likely around 275 USD after tax.
This is from my setup:
https://i.imgur.com/s3AvaId.jpg
Lighting is key. Two cheap colored LED bulbs from Walmart lit my back wall. I am lit by a desk lamp bouncing off the wall in front of me. The room is actually mostly dark. I do have a decent camera hooked to my Elgato but what LTT spent in XLR gear ($900 pre tax between his XLR capture and Microphone) ... That puts his budget way over mine.
IDK if I attached the image right so I also linked a IMGUR link from January 2019.