If you are using CSS, you will still have CSS media queries to say "load an image of this size when on a device with this maximum/minimum size" so you can send

If you are using CSS, you will still have CSS media queries to say "load an image of this size when on a device with this maximum/minimum size" so you can send smaller sized images to devices with smaller screens. Using the HTML markup allows the browser to load the images sooner instead of having to wait for the CSS to be downloaded, parsed, and evaluated. And there is nothing preventing you from selecting a larger image on a 2K/4K display if you have it, or using CSS to provide additional cropping, zooming, etc.