I will add only one other thing that I think is noteworthy. About 30+ years ago we tried having a couple of tournaments that were Ten Ball. ALL the players struggled with this game, with the exception of Buddy Hall, Jimmy Reid and one of two others who frequented the Ten Ball ring games. The matches became so slow that we gave up this idea for twenty more years! Today's players handle Ten Ball like no big deal. Maybe the equipment helps but they appear to me to simply be better players in so far as cue ball control, position play and yes shot making!This is one where we will have to disagree Stu. Efren would have been an even more successful 9-Ball player playing "rollout" pool. It's a closer cousin to the game of Rotation that he grew up on. The more "complete skills" are mainly due to the use of jump cues, with the one foul rule being secondary to that. True, today's best players have mastered this game, but they would need time to learn the previous 9-Ball way of playing.
There was a crossover for a while (several years) where more tournaments began playing "one foul, bih," and the after hours money games were still "pushout" 9-Ball.
There was a lot more variance to 9-Ball when all balls came back up on the spot and the incoming player had the option. And you had this same option any time your opponent fouled. The best players knew how to take advantage of this. Plus you were often shooting from behind the line so you had to execute from distance. As one who grew up playing "Two Fouls by the same player was BIH" I can tell you that I felt I had an advantage over the young shotmakers of my era. I could out move them in a lot of racks. My banking skills won the day quite often. Stu, you often talk about decision making skills and I will tell you they were paramount playing Pushout pool. JMHO as always.
For those who may not be already aware, the reason for the new rules was to speed up the game of 9-Ball and make the matches shorter timewise. All created for TV, thanks first to the McDermott Tour threesome and adopted by Richie Florence for televised matches.