Nobody is asking you to do that, you can assess that for yourself if you're interested in looking at the project, if not, there's not much point subjecting the author to this sort of interrogation.
Consider it rephrased in a way that doesn’t upset you, like “what do you think the advantages of your new library are that outweigh the years of development behind existing libraries?”
Its not (just) the phrasing, its that you’re asking a loaded question the author already addressed in the OP. Your question is loaded because it presumes years of development means anything, and the author already wrote in the OP “im aware there are other libraries, but…”
Consider it rephrased in a way that doesn’t upset you
Consider not projecting emotional states on people you expect to reply to you.
“what do you think the advantages of your new library are that outweigh the years of development behind existing libraries?”
Like the sibling comment says, that's an obviously loaded question. But more importantly - Show HN is for all kinds of projects - from polished commercial offerings to learning projects or scratch-an-itch projects in their early stages of development. It doesn't make sense (nor is it particularly respectful of the author or inviting to new authors) to treat the posts of personal projects like a sales call and present them a list of generic, reflexive checkmarks and requirements questions. A Show HN of that sort is an invitation to take a look at something, provide feedback, chitchat with the developer if you have an interest in the particular topic. If fully-baked things are more your speed, you can just find a Show HN that showhns that.
Cause you're asking me to consider something? Plus it's a forum. So I considered it and also asked you not to be a presumptuous jerk (intentionally or otherwise). That's all.