Yeah, the ubiquity of smartphones and the rise of Facebook and Instagram (post-acquisition) as an open platform for advertisers versus mostly for early adopters/enthusiasts really killed the "fun" of the internet.
Also, I remember how many different frameworks and "rich internet application" technologies existed back then (Adobe Flash, Microsoft Silverlight, Apple QuickTime, etc.). In many ways, the internet was a much more diverse and a much more 'unpredictable' place back then.
Yeah, I'm of the same vintage. Never really felt eternal september impacted the newsgroups I frequented as they didn't appeal to AOLers, and felt it was exaggerated. But it feels real now with engagement metric following content creators and influencers, and the way platforms enable it now.
But then again, I kinda suspect there's some deeper truth going on where your mentioned golden age might be one of the last though?