That's my point, that's not power. Using your hand to judge is like using your face, you'd feel the pain of the strike and therefore it's not a completely accurate way to judge power. Using pads and judging the force behind both strikes is a completely accurate way to judge them, sorry if you disagree but it's just facts.
Roundhouse have more speed and it's using larger area on hit, that's why it "splash" on pads more than a knee. Because It's speed, with roundhouse it's also easier to hit flush a "mobile" targets such as hands even if opponent moving out of the way of kick.
Now knee have less speed but it doesn't lose force as soon as it contact with target, therefore it's more "penetrative", and it's power really shines when you hit less mobile and less movable parts of the body, such as chest etc.
I talk however about knee to the midsection, not the flying one on head-kick height. Something like here from 3:35, I think it could be even more devastating than roundhouse kick to downed opponent aka soccer kick
When I played soccer with my friends some time ago (3 people), the goalkeeper who had 10 goals scored, was getting his butt kicked with full force as punishment (literally), so we had occasions to test out every kind of kick. And running knee was more terryfing to get hit than running roundhouse. Yeah butt is actually pretty resistant and good for such tests xD
Stepping side kicks/front kicks/spinning kicks were mostly pushing us around (but I must note that we were nowhere near level of Scott Adkins when it comes to side kick and nowhere near Rogan as for spinning kick). Roundhouse was really unpleasant, but with knee we were really concerned about breaking something as it REALLY hurts...