Very good analysis here. In the nine ball era, five American players come to mind when considering the route to greatness you've described, and they are Mike Sigel, Earl Strickland, Buddy Hall, Nick Varner and Shane Van Boening. Many of the Asian players have taken a similar approach, including Reyes, Pagulayan, Orcullo, and Bustamante.
What these nine legendary players all have in common, other than a fanatical work ethic, is what the great Johnny Ervolino used to call "a lot of time in the frying pan" meaning that they always seemed to find themselves in heated pressure situations in both tournament play and in action matches, and Johnny always contended that there is no better path to learning how to excel in the biggest spots.
Josh Filler is following in their footsteps, but I think he's the first European, possibly excepting Jayson Shaw, who has placed so much emphasis on matching up with the biggest stars over and over.
Europe's five greatest players that came before Filler, namely Souquet, Feijen, Ortmann, Hohmann and Appleton, legends all of them, went about their development very differently. I wonder if some of the top young Europeans, so many of whom are phenomenal cueists, will begin to adopt Filler's approach to reaching the highest possible level of achievement at pool.
