in most games the difference from 2080/2080 super to 2080ti is a few fps
Important addition: "in most current, and a few years old games". This will start changing as RTX becomes mainstream and older solutions for lighting/reflections/shadowing are gradually phased out.
In my humble experience, for the 6 years since I built my current PC, the games that I've played for a significant amount of hours and that required high horsepower have been GTA V, Witcher 3, Warhammer TW, Hitman 2016/Hitman 2, RDR2. Put together, they make a little over 1000 hours of playtime for me. Since I play on PC I want image quality better than what someone gets on a console, and in the span of the next 6-7 years, I think it's pretty certain that fulfilling this condition will require a GPU upgrade. The open question is will one GPU upgrade be enough and will there be a similar crop of games that will justify such an upgrade for me, because apart from Cyberpunk and eventually KCD2 I don't see them on the horizon, neither on the PC horizon, nor on the possible console port horizon.