This was a boxing match - how did Mayweather prove he wouldn't last in the octagon? Did he try for a single leg take down and it didn't work?
Stoppage wasn't too early. Connor had is gloves down for a solid 30 seconds and was wobbling. Would you rather let him take 5-10 more clean hits to the head before you declared him "beat"? I'll trust a hall of fame ref over some dude on his couch.
In an MMA fight every time Floyd was being hit with a series of punches and dropped his head he'd be begging for Conor to put him in a guillotine choke. Or he'd walk into a knee. Every time Floyd turned his back he'd be begging for a rear naked. Being that he dropped his head a lot and turned his back (more then he should have been allowed by boxing rules) Floyd wouldnt stand a chance in an MMA fight with that approach.
And before you say that it would be a diff fight diff rules so Floyd wouldnt do that. I disagree. Instinct takes over. It is why Conor had to fight the urge to throw hammer fists. There would be no ref to save Floyd in a clinch and that is where an MMA fighter lives