I also joined in 2010-ish, and although the big subreddits have been declining forever, some of the niche ones have improved massively because of the increased number of users. To me, reddit is two parallel user experiences - interesting discussion in niche subreddits matching my interests, and mindless doom scrolling through the big, astro turfed generic subreddits. There used to be more overlap between the two, but the days of interesting comment threads in the default subreddits are definitely gone now.