Any comparison has to be filtered through the lens of professionalism. Americans had the collegiate system but that support, coaches, facilities, disappeared after graduation, a distinct disadvantage in events that you have to mature into. Also it was pretty much just Europe, the US and Oceania. More Asians, South Americans, North Americans, Caribbean and Africans.
For you people who haven’t lived through both, what would football, basketball, baseball, golf, tennis, boxing… any sports except track, swimming and gymnastics, weight lifting, be like if they weren’t PROFESSIONAL sports.
The big difference is the money, which changed everything. The American collegiate system, which is fine if you plan on breaking a record or winning an Olympic medal at 22. Jim Ryun held the world record in the 880 yards, 1500m and mile and had been to three Olympics at 25 yet had to give up future glory after having to turn pro in 1973.
There was really only representation from the US, Europe and Oceania, rarely anyone from Asia, South America, the Middle East, Canada or Mexico. Eastern Europe had a “lifetime” system, instead of college, you went into the military but what they were doing was training.
After the Kenyan successes at the 1968 Olympics, African running picked up but considering that you can retire for life in Kenya (average income $25,000) or Ethiopia (average income $17,000) after, not a major marathon win but a big marathon win.
Money allows anybody (that has the talent) to compete, it brings about coaches and trainers, exercise physiologists, sports psychologists, masseuses, dietitians, facilities, etc. Get more of the above to more people and the logical conclusion is not that there is more talent in the world, but more DEVELOPED talent which leads to improved performances.