This isn't sufficient for all cases. For example a breach could contained a hashed passwords. If you only have the obfuscated passwords of previous breaches you can't hash it yourself to know that the new breach is just a rehash of an existing one.
Data breaches can also contain other things than just passwords. Things like phone numbers, addresses, etc that would also be useful for checking.
Publishing someone’s leaked credentials in plaintext for anyone to look at also isn’t ideal. I mean, yes, it’s been leaked, but we also don’t need to make it easier for someone to get hacked.
Data breaches can also contain other things than just passwords. Things like phone numbers, addresses, etc that would also be useful for checking.