Both terms are functionally useless at this point in history because their meaning is highly contextual and enjoys little to no widespread agreement.
Instead, both are terms where people largely hear what they want to hear. Say ‘I am a liberal’ to two different people, and one thinks you want a more active and powerful state and another thinks you want a smaller and more limited state. And both views are not invalid based on some past usage of the term.
Then you get to the term ‘leftist’ which is even less useful. The left-right paradigm in politics is a oversimplification that made sense in the very specific time and place then it was coined (pre-revolutionary France), and has been shoe-horned into so many contexts since then that a person could be in favor of the exact same policies and considered to be a radical left in one time and place and a radical right in another time and place.
Yet their problems are all functions of their simplicity, and that simplicity is exactly why they kept getting used and overused. It’s so easy to say “I’m a liberal” in a particular time and place and have confidence that, for the most part, the person you’re speaking to now has a pretty good overarching idea of what you’re in favor of. Except as I said, that confidence is misplaced because people hear different things when they hear these terms.