Most of those 450s not reaching 500 is due to the amount/quality of practice not being high enough, not that they are at their "genetic skill ceiling". I can see the maturing argument for 60+ or especially 70+ year olds in that it gets exponentially harder to jump class in pool past a certain age, but even then, the level they reached isn't mostly about genetics to begin with, it was how much practice and table time they put in throughout their life.
For younger adults, lets say roughly 20-60 year olds with average health, average physique and average "pool talent", the true skill ceiling depends on whether you are speaking practically (within the constraints of their life) or theoretically (giving up everything for pool + being rich). Most adults have jobs and families to support, so them putting in 40+ hour practice time per week isn't realistic. Most people also aren't lucky or rich enough to be able to afford or otherwise locate world-class coaching. So these two factors already make 99% of peoples practice suboptimal.
In the case of a typical 30-50 year old 500 or 600 rated player, who has played for 10-20 years, practices 0-10 hours a week and has not done major technical changes in their game for years, it is hard, but definitely possible to jump 50, or even 100 fargo points within 2-5 years. But most people don't have the amount of time for what that takes. And even more importantly, most people don't practice well enough for that to happen. Quality of practice, including making technical changes as needed, is the simple most important thing, which greatly benefits from coaching. So, I wouldn't call talent the deciding factor for most people, but rather the time and quality of practice they happen to get in.
If we compare two players who both practiced roughly the same time over their life, started at the same age, had same quality of practice, but the other ended up at 500 and the other at 700 given their course of life, then talent is an appropriate word. But saying 500s who have already played for years are stuck at 500 for life due to their lack of talent isn't accurate. Sure, there are exceptions, medical conditions can severely handicap your game, but not a single average-health, average-brain 50 year old is hard capped at 500 due to their lack of talent. It just becomes more and more difficult the older you are, especially considering practical limitations of time and quality.
A common example of a 650-700 is someone who started in their early teenage years or even younger, possibly parents owning a pool hall or a bar, put in a lot of practice time in their teenage years and/or early adulthood playing with other 650-700s. Then when they are 30-40, and playing at 650-700 speed, a 600 who started at 20 yo with average practice routines will look at their game and think the 650-700 is so talented. But it is very possible that the 600 would also be a 650-700 had they started at the same age with the same practice throughout their life.
Again, I agree with your arguments for reaching 750+, or 700+ for those who didn't start young. But below that it's much more about practice time/quality.
Bob can officiate. Open for suggestions.
