I guess you're right, but in retrospect we can see localized peaks and declines, so there's something to it.

My favorite version of the Yuga cycle is from some Mahayana sutra, I can't remember which one but it's one of the famous ones, where the Buddha gets nagged by his mother-in-law into shortening the length of the prosperous Yuga's by half (directly caused by the advent of nuns.)