My thoughts are that there certainly are many more "top" players today than prior years. Some of the reasons for this are obvious- the training that occurs from an early age to insure stroke delivery mechanics that, when they become almost 100% repeatable, result in much more consistent high level play on even very demanding equipment. The availability of proper pool training , the internet, the use of the video, all have resulted in many more players that do things "right" on the pool table very consistently - much more so than years ago.
How many of us older guys here WISH that, with our love of the game, we had the same available pool instruction back in the 60s and 70s - I have spent the last two years, finally having the time in retirement, completely breaking my game down and rebuilding it according to "modern" pool teaching techniques- even at my advanced age I have improved at least 30% from a low B to a mid A- the internet and the video replay have been great saviors!
Mosconi had great natural talent - a stroke that moved the cue ball where he wanted it, tremendous final focus ability, and a mind that put winning ( executing under pressure) above all else in life. His dedication to the game allowed him to perform at the highest levels in each of these categories EVERY TIME HE PLAYED.
It takes a lot more than great mechanics to be a great player and a champion in any sport or game. However, more of today's pool pros do certainly exhibit the highest level of repeatable consistency in their game BECAUSE of their adherence to proper pool mechanics- that is the difference in my opinion.