You've been a member since 2007 and you say you're a boxing fan and you need me to tell you this?
Boxers hit harder, much harder. They also have better chins, from years and years of taking (and learning to roll with) punches in sparring, almost every day since they were kids. Even Chael and Bisping both stated from their own experiences of training with boxers, they hit ridiculously hard for their weight, significantly more so than MMA fighters.
And it was perfectly evident in the fight. Floyd - despite not being a big puncher by boxing standards and 20 pounds lighter - was clearly the puncher of the two. His shots had more weight, snap, and torque.
McGregor's in comparison had no real explosion, snap, or torque to them. As I said, glorified arm punches. The gifs tell the story, I mean just look at all the gifs that show McGregor throwing shots, there's really nothing on them. And the shots that did land on Floyd did nothing, at all, which is why Floyd was so comfortable standing right in front of Conor and walking forwards without a care in the world.
As to why he has power in MMA, it's his timing and accuracy in conjunction with terrible chins and defence of MMA fighters. MMA fighters have absolutely awful defence compared to boxers, they're so easy to hit flush. They're easier to hurt too as they're just less used to taking flush headshots, less conditioned for it.
And admittedly Conor's precision and timing is very good, so is his patience and his ability to provoke basic MMA strikers into commiting so he can counter them. And on top of that he has crazy reach. Given all those attributes, it's not hard to see why he's able to have success teeing off on MMA fighters - but in the boxing world, he has no real power at all. Especially for his weight range, 154 to 160 - there are some proper fucking punchers there my god. PillowFists McGregor would be ridiculously outgunned.