Also I remember people's attitudes shifting in some inexplicable ways, suddenly cultural capital seemed to carry much more weight than other forms of capital. For a while it felt like everyone in Tokyo was trying to one-up one another, not financially but through cultural connoisseurship. Strange times but I do miss the general atmosphere, Japan feels like a completely different country now...
I think there's a case to be made that WE changed since then and that it's not purely nostalgia. There weren't the same level of distractions in the pre-internet world (I understand that the Internet existed but it wasn't the attention economy driven behemoth that it is now). People could engage more deeply with things like Video Games and Anime.
People today are conditioned to jump from dopamine-burst to dopamine-burst as they quickly scroll through their social feeds. Those attention alternatives also fill a big part of free time and mental bandwidth, so the time left over that is dedicated to games and other entertainment is limited. Generally our engagement is much more superficial now.
Sure, the internet and social media has contributed heavily to changes in taste and modes of consumption, much like television and motion pictures (and video games!) before that.
The dominance of things like One Piece or AKB48 don't preclude the creation of "cutting edge" stuff, though they might certainly drown those out and make them less visible. I think something similar could be said for the 90s, with the popularity of Dragon Ball and Morning Musume, for example (though to a lesser degree). Still, the Internet has allowed for the creation and popularity of lots of interesting stuff, even if they may not be "mainstream."
One Piece started in 1997, and many argue that it's only gotten better with time.
The Matrix came out in 1999, but so did things like Star Wars Episode 1: The Phantom Menace. I think there's a major survivor bias in your analysis.