I've been on Reddit since late 2005. Before there were comments or subreddits.

My memory is fuzzy, but I remember it getting pretty shallow and memetic since before the Digg diaspora in 2010. And I think it was the popularity of image posts that did it; it was better before image links became popular.

However, Slashdot was already highly memetic since the late nineties, and it was not image-based, so I may be wrong about the effect of pictures.