I could have sworn that a long time ago there was a way to download an entire YouTube playlist by adding the link to it, and the program would automatically populate the queue with all the individual movies, but I can't figure out how to do it.
Am I misremembering or has that feature been removed as the YouTube plugin had to be updated to deal with Google's anti-downloading attempts over the years?

You remember correctly. The feature is still there, but the YouTube API has probably changed and the plugin hasn't been updated.