>My theory is that the high barrier to entry of online publishing kept all but the most determined people from creating content. As a result, the little content that was out there was usually good.
The barrier wasn't that high. Making a site on Geocities, Tripod or Angelfire wasn't that difficult. Writing 90's style HTML wasn't exactly writing a kernel in C, and most of those services had WYSIWYG editors and templates anyway. Few of the people publishing to the web in the 90s were programmers, so the technical knowledge required was minimal.
And plenty of people are publishing high quality content on the modern web, even on blogs and centralized platforms. I follow writers, scientists and game developers on Twitter, watch a lot of good content on Youtube, read a lot of interesting conversations on Reddit. The fact that people publishing content nowadays don't have to write an entire website from scratch has little to do with their personal passions (or lack thereof), whether they're interesting or (and ye gods how I've come to hate this) "quirky." That's like saying writers can't write anything worth reading unless they also understand mechanical typesetting.
As far as the old content goes, of course most of it was crap. Sturgeon's Law applies to every creative medium. Most blogs were uninteresting, many personal sites were just boring pages full of links or stuff no one but the author and maybe their few friends cared about. In both cases, between the old and new web, a bias for the past (as HN tends to have) leads people to only remember the best of the former and correlate it with the worst of the latter.