At current ETH price ROI for this rig is 7 years

Now really why should you invest 4000$ in a RIG that mines 4.5 ETH/year instead of buying 13 ETH coins with those money?
you could mine other coins.
and buy and hodl should not be compared to mine and hodl .
you are leaving out that the rig has at least 50% value when it is a year old.
That said I won't be buying 1080ti's as I have more then enough of them.