I've just coded my latest site using aws but I'm going to be teaching myself terraform in the coming week so I can rewrite the infrastructure as code so I can move providers easily if I ever have any problems in the future.
Terraform is not going to make you cloud-agnostic. If you switch cloud providers, you'll still use Terraform but you will have to rewrite much, if not all, of your TF code.
And even if I don't, I imagine rewriting a terraform workflow is probably easier than taking cloudformation code and then rewriting it into whatever the equivalent is in google or microsoft land. Atm I'm pretty happy with aws and don't see myself moving but I like to have the option if needed.