Ok. In the old days fighters used to weigh in the day of the fight. So if you fought at 160, you're natural weight was closer to that. You weren't going to show up in the ring half dead from struggling to make weight. You contracted to fight at 160, you weighed in 160 the day of the fight, you then hydrated up a couple of pounds. You're fighting at around 163/164 lbs. You're not going to have a big meal before a fight. Plus they fought more often, so they stayed closer to their weight class during that era.
In the 80's a couple of big fights were screwed by fighters not making weight so they switched to weigh ins a day or two before the fight. Now a days, you contract to fight at 160, you weigh in a couple of days early at 160 and you hydrate and fight at 170 or even more. You can have the big meal because now you have time to digest it.
Floyd fought at 147. He would hydrate up to 151 or 154. He made weight comfortably. If he had fought at 154, he would have been fighting opponents who hydrated up to 164, giving up 10 pounds. That shit matters. We started talking about Spence moving up to middleweight, understand at middleweight, you start seeing a lot more 6 footers. That height and reach matters, it's means you're taking more shots from the bigger man. You're taking more shots because now you have to work to get inside his greater reach.
You got two fighters, both are 6 foot but one is slim. He weighs 154 and his people think he's better off fighting at 147 where his height is an advantage. So he struggles to make weight. Now you look at him and say he can afford to add weight and fight at 160 but the problem is there's 6 foot guys at 160 who really weight 172 and struggled to get down to get down there for the weigh in.
If you're adding weight to fight at a certain weight, that's not you're natural weight class.