Its just dependant on the source, you can get good and bad quality UHD, FHD, SD. The worse quality it is, the worse it will look on an UHD TV.
If you are mainly watching Netflix and Youtube and they are available in HD or higher you'll probably be okay.
If those sources however aren't in HD yet (a lot of older youtube content) then it won't look very good upscaled to UHD.
If you are planning on watching your own file rips, I'd want to make sure they are a high bitrate and 1080p as a minimum for an UHD TV.
More value can be found in an UHD model if you alter the quality of your sources to be as high as they can be. Netflix UHD plan instead of standard is one way. Other ways would be Amazon/Apple TV. Regular Blu-Ray/UHD Blu-Rays and or HDR games consoles.
If you aren't fussed about UHD and don't plan on getting sources available in UHD then there is no point having an UHD TV.