I wonder if it's only downhill once you have reached your own point of enlightenment. For me, that wasn't late 00's, but more like late 90's and early 00's. Maybe that was my coming of age.
To me, it's been downhill pretty much before it got started. I'm always feeling "behind" having missed the fun at any stage.
In the late 90's, I attended a talk by Ted Nelson, the guy who coined the term Hypertext. To him, things started going downhill with HTML, and the URL. The gist of his complain is that he wanted links to be bi-directional.
In the 80's, telecom operators were complaining that TCP/IP and packet transmission was a regression over circuit commutation.
So it looks like the internet has progressed through perpetual regression.
The internet is 30-40 years old, and has brought an entirely new paradigm to the world. It has abolished distances, disproportionately increasing the reach of a few.
I'd love to share your optimism that things will keep improving in the long run, but I don't see what you're basing that off.
I like the late 00s/10s because it represents a particular level of refinement and balance of functionality in contrast to earlier eras. As much as I enjoyed the web of the 90s and early 00s, it was still quite nascent and in some ways a bit too basic for my taste.
90s web was fun in a wild west kind of way. Sites were small, but the net in general was slow.
00-10 had a lot of forums in which I remember being very fun. At the same time it brought in the age of popups and ads everywhere.
10+ brought in the age of large social media and the feeling everything was trying to scam you. A lot of the forums that felt special and interesting started disappearing for multiple reasons, but mostly their userbase had moved to FB or something else huge. Then those large sites started moderating anything interesting away.
To me, it's been downhill pretty much before it got started. I'm always feeling "behind" having missed the fun at any stage.