Agreed. I actually just fought and won this battle at work. If you don't want to expose the specific error when logging in, you must either not leak usernames/emails through the signup process either. Otherwise, it's just security theater.
"There is an error with your data..." WHAT ERROR? I've typed 10 fields.
I think a better approach is to rate limit wrong usernames / emails during sign in.
If there was no existing account, send an email with the text: "An account was created for this email address at Example.com. If you requested this account, you may activate it by clicking here: https://..."
If there was an existing account, send: "An attempt was made to create a new account at Example.com for this email address, but you already have an account. If you have forgotten your password, visit https://..."