My logic is that anyone looking at the 3xxx series of GPUs is looking at them for 4k gaming or at a push, ultrawide gaming at a high refresh rate. For the users that do want to game at 4k/120hz, yes, they will likely have to upgrade every generation for a while to keep up with the increased demands which 4k is putting on our GPUs.
Otherwise at 1080p and 1440 I struggle, outside of a few games, to really understand the need to invest in the more expensive 3xxx GPUs when you can grab a bargain like a used 2080/2080ti for a bargain basement price. If I gamed at 1080p or even 1440p (outside of RDR2 and Star Citizen), I just see no need to go higher than an RTX 2080 which will all be sold for a literal bargain with the release of the 3xxx series of cards.
From a value perspective, surely it makes more sense to buy one of the extremely well-priced second hand 2xxx series GPUs (2080, 2080ti) and bag the change.
I honestly see the 3xxx series as a 'must have' upgrade for 4k, super ultrawide and ultrawide (even then, I think a 2080 is more than good enough for 99% of games).