When I hear or say this phrase, it is just an idiom and I donít really think about the meaning of each word. I also think you are correct that we use two words for emphasis.
You probably know already, but the two words have slightly different meanings. A rant could be a logical but excited speech or piece of writing but if someone raves, they might sound crazy and what they are saying probably doesnít make much sense.
Student or Learner