I think you intentionaly try to shift the attention elsewhere. You suggested 3 cards that are not worth the money at the current state of gaming, they are not going to last more than a year and they play current games at medium while you make my suggestions obsolete saying that you should invest in gold to be future proof.
The cards you suggested are just 50 euros cheaper that some of the cards I suggested and the cost/power is a waste. When I buy a PC I want it to last at least 2 years. That is what a futureproof in PC terms means. PC specs change each month so unless you have an unlimited budget, by your reasoning, you will NEVER have a future proof PC.
My old PC stayed with me 5 years because I made it future proof by shopping smart! My PSU of 750 watts haven't changed it yet. I didn't need the power then but I need it now. I bought it at 90 euros then because people did not need that, now it costs about 150-180, come to think of it, all the parts of my old PC were 8 years old except the graphics because I did not settle for "what should I have bought for my rig" but because I bought some parts that I could use after upgrading.
R9 280x does not have below average performance. It is 5% slower than gtx 780 with half the price. Unless you want to convince people that gtx 780 is a "below the average" card that "will be obsolete in 2 months". And yes, future proof means 2-3 years of doing what you want to do without having to spend more money every couple of months or every year round to buy more mediocre parts.
Of course the OP will buy what he thinks is best but suggesting him a true below the average card that only costs 50 euros less in full price (or maybe less if you find an offer) that a good card that can stand pc gaming for at least 1-1.5 year is just null.