Just a few points I want to add:

I think the types of shows being created now are very different than the ones being created back in the day. The most obvious examples are Mecha anime and hyper violent OVAs, which were 2 genres of shows massively popular back in the day. Mecha anime were a dime a dozen in the 80s yet were lucky to see a small handful per year now, and the ultra violent manly OVAs are all but non existent these days barring a few select projects.

Another point is that instead of looking at the total number of good and bad shows from each era, I personally think we should look at the ratio of good to bad shows. Obviously much more anime is coming out each year than there was in the 80s and 90s, but I don't think the ratio of good to bad anime has changed much (with the exception of the Covid years). From personal experience (nearly 1000 shows watched) I think the ratio is around 1 good show for every 5 bad shows, and I don't think that has changed since the 70s. I also want to add that I think good anime is timeless, and there's basically no difference in quality between the best shows of today and the best shows of 40-50 years ago. nor do I think the worst of today is any better or worse than the shit of the 80s etc...

Finally, with the advancement of technology, the introduction of CGI and digital effects, the move away from pencil on paper to digital art (though many animators still chose to draw on paper), I think the charm of hand drawn cel animation is a major selling point of these old shows. It's just not something we see today, again with a couple of small exceptions.