Sorry mate do not agree at all... Have you not seen 4K benchmarks on a 2060S ? You average about 30-50 fps dependant on the game. To me that's not smooth sailing to game on.
When I say 4K gaming is expensive / luxury, I assume running at max settings. You could run it on a 2070S comfortable at mid-high settings or a 2080S at high/ultra settings, or even turning down some dependant if you want 60+ fps or not.
You kidding me? Portal 2 is from early 2011 and so you think 4K gaming is inexpensive?
The above aside, my angle is I'd always suggest 1440p high refresh rate gaming - much more enjoyable (and affordable/realistic) experience than going to 4K imo.