It is always hard comparing different eras, whether old 1st Division to modern Premier Lge, or original Conference of lates 70s (or earlier periods) to today's National Lge top division... pitches, players diet, fitness, etc all play a part...
From a historical numerical point of view of record points or highest position etc even these are hard to judge as like for like when in the 'old days' it was 2pts for a win (not 3) and even league position debatable as over the years there have been different club numbers in each league so more/less teams competing with and also more/less points to play for...
Guess, in short, you cannot compare different eras BUT if we're going to try using statistical data then surely must compare via PPG (Points Per Game Tables)... we do have a great history!