It really depends. Who is the API for? I agree with the sibling comment that showing concrete failures that were caused by or contributed to by poor API design

It really depends. Who is the API for? I agree with the sibling comment that showing concrete failures that were caused by or contributed to by poor API design is effective. If it's a public (customer-facing) API, perhaps you can compare your version to a competitor's: to achieve the same task, what needs to be done? Internally... I haven't had a lot of luck here. Push for it in code/design reviews and sneak a refactor into your PRs? One thing that helps is to have ready examples, so you can say "Hey, I think we need a higher level abstraction here or else we'll be copy-pasting around the same 12 calls every time we want to X, just like we already do with Y API." and your teammates hopefully recognize that pain.