Also I don’t think KDE even uses more RAM than other DEs that are designed to be lightweight. Last time I compared, it used the same or less memory as LXDE.

Yep. KDE is feature-rich, but it's also highly optimized these days, and the RAM usage is actually competitive with the best of them.

You can get RAM usage lower on a very stripped down, barebones system, but if you want a full 'normal computer' desktop experience that has all the things you'd expect a computer to have, you'd be hard-pressed to find one that uses significantly less RAM than KDE. (Yes, there are some that get lower ... but not a lot lower. And unless you're running on some extremely limited hardware, are those extra 20MB of RAM really going to make a difference in your everyday life?)