I can't find it now, but I remember reading about 10 years ago about how long and ugly landing pages convert better. Now, I wouldn't necessarily subscribe to that theory, but it's an interesting one.
Here's a weird take: because the landing page is so vague the user doesn't know whether the app is useful or not so the user will sign up just to take a look at the app to figure out what it actually is. Once the user realizes it isn't for them they bounce. So higher signup rate, higher bounce rate in this case? Total baseless speculation here :D
You mixed up pure and objectively ugly with ugly by design and unique.