It was more a reflection, that "breaking the rules" sometimes creates unique opportunities. Mayweather was the master at getting his opponents to think he was following the rules just long enough to break them. He would start out fighting orthodox them start leading with rights and leaping in with left hooks. Sometimes the right thing to do is the wrong one.
Fighters that pull straight back are asking to get nailed. It's fundamentally flawed but effective, Israel Adesanya does it in MMA (so did Anderson, it got him KO'ed by Weidman), both Klitschko brothers would pull back often due to their height advantage to dodge punches upstairs, and Floyd would manipulate distance using his upper body positioning to bait opponents and then pull back to counter after they reached/overextended. It's used a whole lot in Muay Thai and kickboxing as well.
He definitely fought from a range that most opponents had trouble gauging.
also, movement and angles, he made rematches look different when he could move. The norton, frazier and spinks rematches were very different form when he came in stationary in the first fights. Problem was, man that size and age had to work his ass off to do that.
Yeah, when he doubled up the right hand it threw Silva's read off. Weidman didn't know to do it though he was just trying to touch him out of frustration. That's what he said later on in an interview and that's what it looks like when you watch the KO.
With taller fighters it's even more effective which is why I mentioned the Klitschkos only they wouldn't counter with pinpoint accuracy they would just pull back to defend usually. It's still done a whole lot in Muay Thai at the highest level (to dodge high kicks as well) and in kickboxing and there's still plenty of high level boxers that pull back. Ali used to manipulate distance similar to Floyd by leaning in with his head over his knee to appear closer to his opponents, Roy used this trick as well along with pulling back.
A backfist? I'll have a look, mma Chins are lame.
The left hook put him out but it was actually the backfist type of punch thrown prior that threw Anderson off. Most MMA fighters only train to avoid basic combinations like 1-2's as @DeJulez said. Throwing combos that double and triple up the same hand are trickier to deal with than predictable alternating patterns such as Left-Right-Left. Boxers can deal with it but that's because they're used to seeing it in the gym all the time and in the ring.
boxers don't throw double right hands too often, Hagler exploited that a lot by doubling and tripling up on his crosses, which, with him, he could throw from both sides, no one expects those kinds of punches. as far as lead right hands, Ali deserves a lot of credit for doing that in the foreman fight, making it work, so far as I know, no one did that before him, (probably did but I've never seen it done like that) and a lot of fighters imitated that. Hopkins used it to great effect in the Trinidad fight, that kind of cross is not as powerful as a real right cross because you have to disguise it a little bit and throw It like a jab but it still had enough power to bedevil foreman and Trinidad.
An orthodox stance fighter won't double up too often on right hands but it's something they'll have seen and can anticipate better. Most of the doubling and tripling up we see in boxing is obviously with the lead hand whether they're orthodox or southpaw. Most MMA fighters keep shit really basic and don't even bother double jabbing. They throw lots of predictable single shots that are telegraphed and make basic reads when defending.
