As someone who watched TV in the 1970s, before cable was a thing, I have to disagree here. I think we look back today and see "MASH" and "Columbo" still holding up great after 40+ years and think of it as representative. But nearly all TV was formulaic dreck back then, just like it is now. And even if the average quality level is worse now (which I'm not convinced is the case, but let's assume) the quantity is much higher and there's a large amount of really good stuff to choose from on the right side of the bell curve.
It's true that content can only be created so fast, but it can also only be consumed so fast. Once you have access to enough high-quality content to fill all the spare time you want to spend watching TV or reading or gaming or whatever, having more of it to choose from doesn't improve your experience much.
You're more right than you know.
When there were only a handful of television channels, the content was higher quality than what we have now.
When there were only a couple of dozen cable channels, the content was higher quality than the endless reruns we have now.
When publishing a book went through the big publishing houses, the quality of what was available was higher than it is now where anyone can self-publish and pretend to be an expert.
See also: radio.
Content can only be created so fast. There are only so many talented content creators out there. While the number of media channels has exploded, the number of good content creators has not kept pace. Keep adding paint thinner, and eventually you can see through the paint.
The internet was supposed to give everyone an equal voice. All it ended up doing is elevating the drek and nutjobs to have equal footing with people who know what they're doing and what they're talking about. The quality is drowned out by the tidal wave of low-grade content.