That's maybe the theory, but in reality, the only thing Ansible hopefully is, is idempotent between playbook runs - but there are no guarantees there, at all. Only in very simple setups things can be fully declarative in it's totality.

Don't have much puppet experience, but I can't count the times anymore that I've had to add steps to playbooks just to determine stuff used in one of the following steps. The other option was to write a snowflake Ansible module. The individual steps/plays might be declarative, the playbooks are not.