That strikes me as the likely plausible culprit. The one that keeps tripping me up in unrelated domains is that the multithreading story is not easy or fully s

That strikes me as the likely plausible culprit. The one that keeps tripping me up in unrelated domains is that the multithreading story is not easy or fully supported by libraries and tooling. We've run game engines and utility binaries (ffmpeg, zip, etc.) in the browser and they're super slow because of this.