Just because all the greats didn't think "load/unload the center" or "load my scap" or "set my posture" or "stay connected" that doesn't mean it's not what they were learning to do. In fact, that is exactly where their trial and error process took them. Today, we can shorten that process by paying attention to these "better defined" terms.
Over many many reptitions they learned (the hard way) about loading the center, creating momentum by caring the load forward and rotating with connection. Of course, the words we use now weren't used by them.
Only recently have these basic core movements had the new words connected to them. And, it was done by N y m a n. He didn't discover how to hit. But, he has learned to properly define the movements. Defining them so that what looks the same now has more meaning. Examples:
What is now "carrying your center".....was stride back then. They look the same to the uninformed but are very much different.
Counter rotation or inward turn is now scap load. Not just a new term but a better explanation of what is going on.
Stance then is posture now.
Batspeed then is bat quickness now.
Each of these contain more information than the original term. Each better explains reality.
This applies to today's hitters also. When the new terms were coined they all were already advanced players. Far into their own trial and error process.
That's why you don't hear Gwynn, Bonds, Pujols etc use the terms. They learned the old fashioned way. They didn't have their trial and error process shortened by a coach using these new terms.
However, give it a few years. Let todays youngsters growing up on these terms get old enough and see how they describe their swings.
As far as in what order did the greats learn their swings. They all suffered through the trial and error of more batspeed = less quickness. More quickness = less batspeed. I need quickness but my speed suffers. I have great speed but I don't have reaction time. Back and forth. Forth and back. Until it all came together.
IMHO there is no substitute for swing quickness. Swing quickness will get you playing time when you're young. Play defense and get hits = playing time for youngsters.
Now, learn to add some batspeed to send those hits further.
Compare that to the batspeed kid. Hits a long fly now and again and doesn't catch up on many others. Constantly swinging at bat pitches. Doesn't have the reaction time needed because his swing takes too long to execute. His long flys better be real long and pretty often to make up for his low OBP. And, unless he "trades off" batspeed for swing quickness his days are numbered.
Learn quickness first then learn speed.