It seems reasonable to have distinct tags for ansible, ansible-tower, and ansible-galaxy, as they are fundamentally different features/areas of the Ansible family.
The Tag ansible-playbook by itself is unnecessary -- any post with this tag should also have ansible.
It is like having separate tags for ansible-syntax, ansible-modules, and ansible-conditionals, much too granular. It does not make sense to have a separate tag for questions that are playbook related.
The precedent for this exists with bash and the symbolic-tag bash-scripting. Shouldn't the same work for ansible-playbook?