That’s not as effective, since it can’t block anything that’s hosted from a hostname that also serves regular content without also blocking the regular content. It also can’t trick websites into thinking that nothing is blocked and it can’t apply cosmetic rules. I use it for my devices, but in browsers I supplement it with uBlock Origin (or whatever is available in that browser).
But 2K and 4K do refer to the horizontal resolution. There’s more than one resolution that’s referred to as 2K, for example 2048 x 1080 DCI 2K, but also 1920 x 1080 full HD, since it’s also almost 2000 pixels wide. The total number of pixels is in the millions, not thousands.
For 4K some common resolutions are 4096 x 2160 DCI 4K and 3840 x 2160 UHD, which both have a horizontal resolution of about 4000 pixels.