So no unless it is mandated that all countries have a fixed athletic budget for olympic athletes it will never truly be a level playing field
How would you differentiate that budget for a country like China, that has a billion people and say Jamaica with just a tiny fraction of the population. If the budget is decided by a countries population it massively advantages those countries with large populations, if it's fixed no matter population size it advantages the smaller countries.
In answer to the original topic, I think there is a lot of "evening out".
Some of this is down to the high number of athletic (not just track and field) programs that US colleges run. The large numbers of non US citizen sports scholarships being given by US universities means a lot of these countries (and their athletes) are benefitting from the massive $$$s in the US college system.
Some is down to a large number of coaches (mostly from Eastern Europe) now being able to travel to other countries to help them develop their programs.
Some is down to countries deciding to spend a lot of money on their sports programs. For example Australia has one of the best (probably THE BEST) developed sports programs and their results, compared to their population size , are quite stunning. The Aussies also benefit from a great climate that encourages outdoor play for kids, and a society that also values fitness and athletic ability highly. As a nation I would think the Aussies are probably the fittest and most athletic in the world.
A final contributory factor , IMHO, is the break up of the former Soviet Union. Previously there was the "big two" USA and USSR . Now we see China and USA as the big two, but if you added up all the medals of the former Soviet Union you would see it would have been a "big three", but the competition between the former Soviet union states (each desperate to out do the others) has meant that individually they are stronger than they would have been as a single unit.