Yes, anarchists and other libertarian socialists, if any distinction is to be granted, should do all they can to shift the Overton window, and to counteract the systematic exclusion of leftism from mainstream discourse and participation, particularly in the United States, where everyone knows of the Liberterian Party, but extremely few understand the term, nor even the concept of, liberterian socialism.

Leftists need to focus more on being understood by the average person. Redefining words and trying to take back redefined words doesn't help that cause though I make an exception for "The Left" "Leftist/ism" etc.

Shouldn't anarchists be taking the word "libertarian" back from ancaps and other propertarians?

Yes, lets, wherever that's happened. Some places have not suffered this usurpation and perversion of language.