On the password1, password2, password2! flow, yes this happens and is bad, but not everyone is like this. I would say, any change (even a weak one) to a compromised password helps (even a bit). Because it requires attackers to test more passwords, providing more opportunity to detect them.

I agree, on moving the weak point to certain service providers when doing this.

Unsolvable: hm, but isn’t the idea to make it more secure, not necessarily solve it completely?