Creating something good and open source is not a delusional dream imo. Whether it catches on is another matter. But even a relatively modest following is a very fine result. I first learned of lichess some years ago when I was looking to make my own chess UI and discovered their high quality open source chess library
The special thing about Lichess is not that it's good and open source, but that it actually pays an okay-ish salary to work on fulltime, while upholding all those lofty goals. It's an actual job. Without the whole thing being paid for by FAANG.