Short ish answer.
No their 20min power is not 400+w…
It’s basically a random number generator.
Unless you’re talking about a very large lean athlete, it’s very rare for someone to produce over 400w for 20mins. This would have them riding at incredible speeds.
I’ve met a few riders capable of it in real life. All of them were elite or professional athletes. If they aren’t elite, they are just very large riders. As a w/kg measurement 400w for 20mins is not very special at all, if you weigh 100kg/220lbs etc
Sadly the kg part of w/kg is a thing…