Who are the opponents of Tazio Nuvolari? The mantuan during his long career has competed against some of the greatest champions of all times. They have written the beautiful and incredible pages in the history of the motor-sports.
It's important to emphasize as Nuvolari has been confronted with generations of various drivers and on various means (cars and motocycles): in the long years of activity he "fights" with champions at the end or at the beginning of the career, and with others that have lived with he the entire agonistic period.
The names that you find in this page are enough in order to understand the level of competitiveness of the races of that period. A similar "concentration" of champions has not never more been reached in the periods that followed.
We have to consider also that some racing cars were powerful like the modern ones (for example the Auto Union prepared for the world speed records has a max speed of over than 450 km/h - 280 mph or the Mercedes Benz that has more than 600 hp of power) but that had characteristics (tires, chassis etc...) that made them true "monsters" to drive!
Moreover the circuits were very long, dangerous and stressed over the human limits the drivers (and the cars!).
If we consider all these variables we understand as the period between the two world war is more legendary and "extreme" than the others.