You CANNOT get into PC gaming with that mentality. Just because a GPU you buy right now isn't fast enough to run next year's games maxed out won't make it any slower for the games that are already out, and nobody can just tell you how long your hardware will actually last....what if in just a year or two your PSU takes a shit and takes all your components with it? What if you accidentally damage/kill a part with ESD? Would you go out and buy the same part, or upgrade to something newer? Stop concerning yourself with "future proofing" as there is no such thing with gaming components, just try and get the best value for your money and be happy with that.
Also, you're never going to get an answer like the one you're looking. You're basically looking for game devs and GPU engineers to drop by and say "yeah, you can expect to get this kind of performance on this hardware with this software, which should stay relevant for this long". GL with that.