Did you see Floyds face post fight? Not even a tiny scratch on it. I would say that is decent evidence.
You would be very wrong. Not decent evidence. Terrible evidence.
And the original question was punching in UFC vs. in Boxing. Not Floyd vs. McG. So you're not even addressing the original question.
Evidence would be something that measures the force of punches thrown by UFC guys versus Boxers. Marks on face at end of fight don't show that. When the "Big Rig" fellow fought GSP, Big Rig looked like he came from a picnic. GSP looked like somebody had worked him over with a pipe. But that's not evidence that GSP doesn't punch hard.
Likewise, Floyd worked him over for 4 or 5 rounds after he was punched out/gassed.
What the fight showed was 2 things:
1. Floyd is a demonstrably better boxer than McGregor.
and
2. The difference in boxing skill/talent between Floyd and McGregor was not nearly as great as most boxing fans believed and not nearly as close as most UFC fans believed.
I know that this thread is all boxing fan boys and UFC fan boys, so nobody is going to be reasonable, but I'd be curious to see an actual scientific study on punch power. I have no doubt that boxers would punch harder, on average. How much harder is the question.