Walter Johnson is, without question to me, the greatest pitcher of all-time. He absolutely dominated. That is greatness, his level of achievement was outstanding relative to his peers.
His competition wasn't. That is part of the reason he is the greatest of all time. Along with the diluted talent pool of that era, you have the basic realities of how we have substantially improved athletically since that era. We're bigger, stronger and faster now then we used to be, and that is a trend that has been consistent since we've had any way reliable means to measure it. We lift more weights, we run faster over any distance interval, we jump higher, we throw things farther. We have also have highly trained athletic trainers to rehab and prehab injuries and athletes train year round, they aren't selling cars in the off-season to supplement their salaries.
If you put him in a time machine and stood him side by side to Justin Verlander I don't think it would be a competition.
We had this debate in the chatbox the other night over if Bob Feller threw 105 mph. Bob Feller was 6 feet fall and 170 pounds. Walter Johnson was 6'1 and 200 pounds.
Go ahead and look up the hardest throwers in baseball right now. Here's a shitty bleacher report list that's a couple of years ago.
http://bleacherreport.com/articles/...e-25-hardest-throwers-in-the-majors-right-now .
Go through the top 10 or so and look up their height and weight. By and large we are talking about guys who are 6'3 + and around 220 pounds. You want to add in some guys like Joel Zumaya and Roger Clemens you get the same trend. Are there some exceptions? Sure, but they're usually relievers and they often throw their arms out. You want to credit Nolan Ryan (still 6'2, but only listed at 170) as a freak... ok.
This might be a shock, but being taller makes it easier to throw hard, the same way that being tall helps you generate more power when you swing. That observation is also consistent with data posted at fan graphs which shows a steady rise in average velocity every year for the past dozen years or so. It's also consistent with every other athletic event we have reliable recordings for.
Baseball is more then velocity. Pedro is my choice and he didn't throw as hard as Randy Johnson. Because pitching is more than just velocity the best pitcher could be from the 60s or 70s, unlike football in which I don't many players from anywhere before the 90s would crack a modern starting lineup. I think in the recent past the athletic gap is still small enough that those players are relevant, and they also had to play against a full talent pool (black/latin players).