But what about screencasting? It's my understanding if I use HDMI to HDMI smart TV the picture quality maxes out at the laptop screen quality, so I would want the 4K on the laptop inorder to have a 4K picture on the TV. Correct?
I’m sorry but this article misses the point of 4K screens altogether. Going by the logic of the author, sports cars don’t make sense either because speed limits exist. Yet the handling of an 911 is leagues better than an average sedan at the same speed.
Similarly, the point of 4K isn’t to make text smaller. It’s to simply make the same text crisper. The 300% is not 100% is an unfortunate outcome of the laptop manufacturer factory settings. If phone screens were running at “100%” the text on that too would be terribly small for most people. 4k is not “make text small”. It’s “make everything sharper”. A laptop screen at 13”, 4K, has a lesser ppi than an average iPhone. It’s a software configuration issue.
Your first mistake was going with a 13" laptop and 4K. I'd never have done that. I DO, however, have a 15.6" Dell with touch 4K and, as a commercial photographer, when combined with AdobeRGB, I'd never go back to FHD. Why, you may ask? No jaggies when enlarging a photo to 200, 300, or even 400%. Clients sometimes want to see the details on a garment or product I'm shooting, making sure they can see everything. 4K also offers finer gradation and movies in the hotel room after the shoot really pop. FHD screens are plain ugly beyond 100%. So, 4K is definitely worth it, but only if you choose a larger screen; 13" is barely beyond tablet territory.