Not to be a Debbie Downer, but we don't really know about these velocity claims. Seriously doubt Feller or Ryan threw that hard (but hard relative for their era, yes). Those pitches weren't measured the same way they are today, just in hindsight by a scientist who has a theory, but was not there to actually measure the pitches. Even he (Gregg Franklin) said, "So is this definitive? I don't know. I don't think we'll ever really know who threw the hardest, but it's a lot closer than the original numbers suggest."
And, the movie "Fastball" was made in 2015, nothing new here (cool story, if a bit sensational, as would be expected. I watched it several years ago at the Society for American Baseball Research convention in Miami). Fast forward to now when guys are throwing on average with the highest velocity (92.5) of all time. It simply does not statistically compute that at least one contemporary player would not be throwing harder than 107-plus like Ryan and Feller – in other words, were Feller and Ryan mega-outsized outliers for their eras compared to today's best fastball pitchers? No. Even Chapman's 105.8 is below the Feller and Ryan claims, hard to believe.
Yes, much depends on where you measure it:
https://www.baseballamerica.com/stories ... the-years/ ... But the point is that you can't compare across different tools used in different eras for measuring fastballs, and what we know today as the most accurate one is the current MLB Statcast system. Before that, it was the Pitch/FX system, before that the Speedgun, Jugs Gun, and so on, all with nuances. No consistent method across the years in measuring fastballs.
BUT, and this is the key point, human sports and athletic performance has advanced so much in recent years that these players are optimized for their talents much more than players of bygone ages. We live in an era of freakish athletes who are better developed, trained, given better nutrition, all to reach their potentials. Doesn't mean the "game" is better (I actually prefer the old school game). Genetically, I believe humanity has always had freakish athletes, of course, but not necessarily the knowledge to properly develop them.
Also, anecdotally, if pitchers many decades ago were throwing SO hard, batters would have immediately begun wearing batting helmets. The fact that batting helmets weren't worn for almost the first 80-90 years of play tells you pitching velocity was not that high for a long time. Batting helmets came into use in the '50s and '60s when velocity began rising.