Logically speaking, "flat chested" girls are more related to the decline of modern day anime that people complain about than "healthy" girls.
The number one cause of this drop in quality that people say is happening, is the moe craze. Marketing to cheap ass otaku and not actually putting in any effort. I'm not saying LOL OLD ANIME WASN'T MARKETED TO THE AUDIENCE, but I am saying that moe is the bottom-of-the-barrel bullcrap that's cheap to produce and sells hard. And flat-chests are much more directly related to moe than large breasts are.
Large breasts have always been anime, now and in the past. Flat chests are directly linked to decline of quality in modern day anime.