DCP,
You probably already know what I think, but I'll repeat it anyway. I think Mark is also "top-of-the-line" when it comes to instructors. I have taken lessons from 2 touring professionals and they were really helpful for strategy, showing all types of interesting shots, mental game, etc. But it wasn't until I had lessons from Mark and Jerry Briesath that my game exploded (not that I'm any world beater, but I'm getting respectable; and certainly better than I ever imagined). If you follow their instruction, you can develop a very precise, very repeatable, very tension- and pressure-free stroke. With this kind of stroke any one can become an "A" player (JMO) with practice. I tried on my own for 15 years and never found that kind of stroke or proficiency. Pool is amazingly fun once you develop this kind of stroke, I wish I had found it 35 years ago. I know there is more than one kind of stroke that can be successful, but if yours is not giving you the results you expect, then SCRAP IT, and let Mark build you a new one. With the kind of time you are devoting to practice you should be playing in the tournaments, not watching them.