The ultimate fighting example is more open because it welcomes all martial-arts backgrounds and you can specialize or be well-rounded. It's a fight, you can stand-up or take someone down. You can fight how you choose. It's history is literally an open contest of people fighting how they choose.
In boxing, it's only the sweet science. Connor's boxing experience is simply boxing for mma. It's totally different. You don't see people training straight up boxing because they would be left vulnerable to takedowns. It's more that they learn how to punch properly and throw combinations that are effective in an mma environment. Arguably the hardest boxing skill to master is defence, which in it's specialized form would not be very useful in the octagon especially against someone who may clinch strike or take-down.
MMA is also a much newer sport where it's beginnings were literally a pure karateka vs a pure BJJ guy or pure boxer (wearing one glove) vs an olympic style wrestler. Boxing isn't like that and has never been like that, it's just boxers who box.
The other thing about the MMA example is there are always 3 rounds and 5 for a championship, in boxing it goes 4,6,8,10,12 (and 3 for amateurs). So in MMA there is nothing to take into consideration there.
Boxing has a rich history with a massive sample size and major veteran experience when it comes to looking at a match-up on paper and in person and determining if it's safe and legit. It's my belief that if MMA was more obscure or illegal in the USA or they didn't get paid or it was a very small niche sport that it would never happen. The only reason this is getting sanctioned is because of the popularity and influence of the athletes involved and the massive amounts of money involved.
Anyone who follows both sports as I know you do, knows without a shadow of a doubt that this will be a 1-sided embarrassment for CM. I think Max Kellerman has a point when he says that he thinks Connor won't even land a single punch. And all of this leads to my aggravation that Floyd gets a free W to make that new record against a guy who has never boxed. It's total BS. Why did it HAVE to count as a pro boxing fight? I'm sure they could have found a way to call it a Boxing challenge or something like that to avoid tarnishing the sport's legacy.