Glad I could help clear things up for you a little! I was taught the same as you. But I would say that I've fully come around to viewing them as mostly useful and sometimes borderline essential. One example that I came across recently that I didn't really explore here that makes a pretty compelling case for their use is instances like this: the piece was titled/subtitled:

"‘HAIR,’ Home, and the Vietnam War"

"The anti-war Broadway musical that shocked our nation, while shaping my convictions and giving my feelings a place to call home."

In the title, initially it didn't contain the Oxford comma, and I thought that that has a mild way of grouping together "Home and the Vietnam War" as an almost singular entity. Whereas in the subtitle, while it is a list of three things as well, I thought that "shaping convictions" and "giving my feelings a place to call home" were similar enough to be grouped together, like "peanut butter and jelly" or "hopes and dreams."

Omission will rarely lead to confusion, but I would certainly argue that inclusion can add clarity in many cases! Thanks for reading, Anthony.