And when you look at Mayweather's defensive technique, he also:
a. uses lateral movement to move constantly away from his opponent's power side (e.g. he would be moving to his left to avoid McGregor's left hand);
b. has his chin buried into his collar-bone/upper chest/shoulder;
c. has one upper arm locked to his side to avoid body shots with the forearm protecting the sternum, etc and
d. has the other hand protecting the other side of his face but with the arm ****ed to counter-punch
Added to that he is/was one of the fittest guys on the planet and had the reflexes of a snake
He was literally the prime example of hit without being hit whilst McGregor is all hit
You seem to know your boxing, I'll give you credit there although you've missed a couple of things that Mayweather did such as using his glove to shield the eyes of his opponent while ripping to the body, or using his elbows against his opponents throat whenever in a clinch, or collapsing at the waist to move under punches, or as you point out, using the shoulder roll technique to ultimately get inside on his opponents without taking damage.
But you miss vital points about tucking your chin into your collar bone, and having the shoulder roll technique, and having a side on stance like Mayweather uses.
a. The shoulder roll technique will completely obfuscate your vision to see any kick being thrown, you would be picked apart by leg kicks and head kicks at will by your opponent
b. Having a sidewards stance is great in boxing, because you're able to move and pivot off of either foot and you don't have to worry about having your front leg kicked out from you, or being swept for a take down
c. Moving constantly away from the power punch of a boxer leaves you further open to what I've mentioned in Point A, leg kicks. Distance is a completely different beast in kick boxing as to what it is in boxing.
d. Mayweather always fought absolutely defensively, McGregor always fights absolutely aggressively.
e. No boxer in the history of boxing could lay claim to being 38 and still not being hit against elite level fighters, not even Pernell Whittaker, Floyd was one of a kind, so comparing his boxing skills against a UFC fighter isn't a comparison worth making, it would be like asking Floyd to compare his dirty boxing against a jujitsu clinch, no point.
If you're saying Diaz exhibits any skill in the same level as Floyd on defense, I'd point you to the fight stats that had him taking 20 significant strikes in one round, Floyd doesn't take that many in five fights. If you're saying that McGregor should adopt a shoulder roll technique, keep his chin tucked and his power hand tucked onto his chin too then you don't understand enough about kick boxing to know why almost all fighting stances in kick sports are much more open, fluid and do not have you tucking your chin as much.
Full credit to Diaz, where he was unbelievable was how quickly he ripped through McGregor on the ground when McGregor foolishly took him down, he busted him up quickly with ground and pound and the moment an opportunity was there he sunk in a deep choke, that was brilliant ju jitsu and somewhere Diaz has been amazing for years, somewhere he should actually fight more as his stand up is no where near as good as his ground game. Diaz is a good dirty boxer, but he's not a good boxer. He throws arm punches that leave himself open for countering and as I've pointed out, having that many shots landed on your skull isn't usually a recipe to winning any fight unless you go back to intangibles - durability and endurance, i.e Antonio Margarito beating Miguel Cotto in their first fight.
