Device screen size isn’t the same as browser viewport. A 360x640 mobile has just a browser viewport of approx 360x540, depending on OS, browser, scroll, themes etc. And a 13" laptop with a 1366x768 screen could have a viewport as low as 1351x570.
It’s impossible to tell the exact viewport dimensions for a given screen size, except for mobile devices where the viewport width will most likely be same as the device screen width.
It’s nice to have the list of devices to choose from in the RDM and for now I agree to keep it. However for better web development I think the tool should focus more on custom sizing of the viewport and saving custom sized viewport setups. Make it really easy and dial back on the device screen sizes.
What do you all think?