I think you are failing to consider an important element here, which is that TV's have come a long way in the past several years. Even if we operate under your logic that upscaled 1080p will never look as good as native 1080p, there are other features in modern TV's besides resolution that contribute towards their superior image quality. Full-Array Local Dimming, for example, can make an astounding difference in how good an LED TV looks.
Actually, I think you don't realize how good some of the older videophile-tier TVs were. The Sharp Elites were FALD -- and had far more zones than any modern LCD except for the Samsung Q9FN and Sony Z9D. The 60 inch Sharp Elite had something like 240-300 zones and the 70 inch had 600+. There is a reason it cost $8000 at the time. The modern Sony Z9D(best LCD TV that exists) has 648 and the Samsung Q9FN has 480. There are some avsforum posts comparing the older Sharp Elites to newer TVs, and while the newer Sony FALDs(and surely the Q9FN) do perform better, if you find a Sharp Elite for $500-600 and the panel is in good condition, it's going to perform significantly better than any of the cheap TCL/Vizio/etc garbage that you are going to find new at this price point. Now, the reliability of a 5/6/7 year old LCD TV is another story but the performance is above average even by modern standards.
Same goes for the plasma -- The F8500 is going to beat everything but the top tier modern Sony/Samsung FALDs and OLED on black levels and image quality. And for motion quality, well LCD and OLED still struggle to compete with plasma in that particular area due to sample and hold.
Now this is all for SDR 1080p content -- of course the big benefit of modern TVs is 4K and HDR. But if you aren't gonna watch that content, it doesn't really matter. And I'm not degrading the modern TVs, HDR is a huge, game changing effect as far as I'm concerned. It looks SO much better than SDR that I consider it equivalent to the improvement from SD to HD, and much better than HD to 4K.