Your theory on there being a time when board game design improved dramatically in a short period of time is correct, it’s just that you have the time wrong. Basically anything posted to this thread that’s about 1995 or later will be indistinguishable from something published today in terms of design quality. (Production quality has improved since then, of course). There’s a ton of games of similar quality as E&T from the same time period, and from a lot of designers rather than just Knizia.
While if you look at the stuff posted in this thread that’s from before that, most of it is really rough and won’t survive a group that doesn’t have nostalgia for a specific game.