I wouldn't dispute that generally the competition is closer today than at some different points throughout history. It varies. I will state that much of today's closeness is an obvious manipulation. Actual speed differentials show that if races were conducted and officiated more as they were during those historical periods mentioned, teams like the #78 in 2017 and the #4 in 2014/2015 had the speed to decimate the rest of the field. Dominant cars are held in check by increased cautions, stage breaks, double-file restarts, lucky dogs, wave arounds, etc. NASCAR may be trying to achieve parity by making the cars closer in actual performance, but they've had far more success simply forcing the races to stop more often to stack everyone up. They could throw the yellow every 10 laps and restart four-wide, and this would lead to more statistical lead changes and closer finishes.
Tolerance for these measures varies. Some would rather watch a 'purer' race, some don't care as long as the results are more to their liking. I tend to not be an ends justifies the means person.