1080p looks blurry on a 2K screen because it isn't an integer scale of 2K. 720p (2x2 pixels) should actually look better on your 2K - given that all noise reduction and artificial sharpness are turned off - since the hardware is essentially line-doubling instead of upscaling. 

There seems to be some confusion about upscaling amongst those who aren't into the retro gaming scene at the moment. Lower-res content looks its best when played on a screen that fits its resolution perfectly. Good scalers can bring those sources up to a larger pixel count with negligible artifacts, while most scalers seriously degrade an image. 

1080p looks okay on most 4Ks because 1080p and 4K are integers.

Where things (generally) start to get ugly is non-integer scaling. For example, 720p on a 1080p screen, 1080p on a 2K (1440p) screen, and 2K on a 4K (2160p). Those resolutions don't divide evenly into one another, and so the scaler needs to "guess" at extra pixels instead of simply doubling (2x2 wide) or tripling (3x3 wide) the pixels of the source content. 

That image is actually a perfect example of how much information is generally lost during bad upscaling. The "normal" image has sharp pixels and great contrast. The upscaled image, by comparison, is fuzzy and contrast is low. 

I would recommend the RGB master series by "My Life in Gaming" or anything by Fudoh for more information about upscaling. 

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For anyone thinking of picking up a 4K TV for use with older consoles, please do your research on how those televisions handle analog signals and if they feature a fast, decent scaler. For those who already own a 4K and aren't happy with the picture, and/or lag, check your system settings. Turn off any artificial sharpness, edge enhancement, noise reduction, etc. Look for a "game mode" if available. That should leave the picture from your older consoles generally unmolested. 

I know you are just trolling, but for those interested, the human eye resolves visual input at around 12960p depending on age.

i.e. 23040x12960, i.e. 12x the resolution of 1080p, 6x the resolution of 4k.

No, actually we're talking about downsampling, in this particular case downsampling from 1080p to 720p touch screen. Pictures you showed doesn't have anything we staffs we talking about here.

Lol, what evidence!?

Every TV has upscaler, but that's not native upscaler, while for Switch you have games running at native 720p in portable mode and on TV at native 1080p.

If relly doesn't use extra power of Pro, why those features are not available on basic PS4 but just on Pro model!?

From link that you posted:

"Primarily, Overwatch players can expect improved performance in 1920x1080 resolution on PlayStation 4 Pro. We've also made several minor improvements that take advantage of the console's capabilities, including better texture filtering and UI enhancements."

Bottom of line, Switch in portable mode is meant to be 720p handheld, that's why it has 720p screen thats why there is no any need for 1080p screen and thats why Switch does not have 1080p screen, it doesnt need it, very simple. Also for record, all people who actually tried Switch are saying that screen is great, games look very sharp and bright.

I'm not disputing that.

What you are talking about is Nearest Neighbor resampling, which allows you to keep the image nice and clean and fresh.

But when that option isn't available... You can still gain better results than native resolution thanks to video scalers having built in functionality that can do a few post-process passes, such as blurring, sharpening, interpolation, that sort of thing.

Good scalers shouldn't degrade an image, introduce artifacts or "damage" an image if done correctly.

It's an extreme example and not a perfect upscale, meant to accentuate the differences.

There are also different types of upscaling. You can take a Progressive image and rebuild it into a "higher resolution" interlaced image, one of the most popular examples was Grand Turismo 4 on the Playstation 2... And the improvements was striking and universally praised.

You must be confused. I have been talking about upscaling a 720P game to 1080P this entire time.
Remember how I wanted a 1080P screen in the Switch? Even if games aren't being rendered at that resolution? That's called upscaling. Not Downsampling.

If you think a TV's upscaler has the same capabilities as the Scaler built into the Switch, then you are kidding yourself.

The Switch is going to be upscaling a ton of games whilst docked to 1080P, if you think every Switch game is going to be 1080P whilst docked, then again, you are kidding yourself.

I want the same on the Portable screen.

Good question. Probably because the HDMI 1.4 port is limited to 30hz at 4k on the regular Playstation 4. Overwatch is a 60fps game.

Or Blizzard opted not to backport it and downscale the UI even though both versions of the game are 1080P... On the Pro, the game is upscaled.

Correct. The Switch is a 720P handheld. Mostly because Nintendo decided to cheap out.

720P is unacceptable in 2017. It's very simple.

What good would get running 720p game on 1080p screen!? Nothing, it's basically same like running 720p game on 720p screen.

Lol, Switch does not have "built in" upscaler that makes native 720p games runing at native 1080p, but games will built in way that will use extra power of Switch that became available in docked mode for higher resolution in TV mode. Games are built in way that will run at 720p in handheld mode and at higher resolution in docked mode, something similar like PS4 Pro is doing compared to basic PS4.

You cant get 1080p games on Switch in portable mode because hardware would need to run at much higher clock at 1080p resolution, that basically means much worse battery life than it actually is. You do realise there is reason why Switch GPU clocks are 40% lower than those in docked mode!?

That doesn't have anything with "Nintendo decided to cheap out", it has with making best solution for product like Swith where you need to pay atention at battery life also. Actually easiest way would be for Nintendo if they made Switch in way that games runs at exactly same way at 1080p at portable mode and docked mode at same clocks, but reality is that battery in that case most likely would be around 1 hour.

Of Course that 720p screen is very acceptable for dedicated gaming device in 2017, and impressions of people who actually tried Switch proves that, like I wrote, all people saying that picture on Switch screen is great, very sharp and bright. For record Switch screen has similar pixel density like iPad Pro.

240p is native to your 3DS. You think 720p looks as good on a 2160p screen? What does your 3DS have to do with a 4K screen? The OP is talking about his 4k not your freaking 3DS.

Wrong the resolution of 12960p is a rough average based on the active surface area at the back of the eye, that deteriorates with age, nice try though.

p.s if you're going to say 12960p is wrong you might also want to edit the 23040x12960 but too..  doop de doo

For me, even though I have a 4K TV, 720p is "HD enough". Yes, I'd prefer higher resolution but it's okay. 480p or whatever Wii was was unacceptable. I'm happy with everything Xbox 360 and higher.

My TV is only 1080p, but I still regularly play Wii games in glorious 480p, and honestly, they look fine to me. 

Obviously it doesn't look as clean as Wii U or 360 games, but it's completely playable and doesn't significantly detract from the experience for me.

We have been over this already. I am not going to keep repeating myself. Go back over my prior posts.

It does have an upscaler. Otherwise whilst it is docked, the Switch wouldn't be able to upscale it's games to 1080P.

We aren't talking about running games at 1080P. Do keep up.

Nah. Nintendo cheaped out on the screen.
They even cheaped out on the Tegra chip, but that's a discussion for another day.

The iPad Pro has a higher pixel density of 264 pixels per inch.
The Switch has a pixel density of 236.87 pixels per inch.

The iPad Pro has an "okay" 2048 x 1536 on the 9.7" model and 2732 x 2048 on the 12.9" model.

iPad Pro is superior... And that is saying something considering the iPad is far from the best, but is also one of the most expensive tablets.

And that's only the resolution. Remember, Switch cheaped out and is isn't using something like OLED/AMOLED.

720P is a last century resolution, it's not okay in my tablets, it's not okay in my phone, it's not okay on my PC, it's not okay on my TV. Why would I think a Nintendo device should be the exception to the rule? News flash: It shouldn't.