Have host_vars or group_vars greater precedence than include_vars counterparts.

tasks__main.yml

---

- name: Include vars based on various criteria, into platformspec hash.
  include_vars:
    file: "{{ item }}"
    name: platformspec
  with_first_found:
    - "{{ ansible_distribution }}.yml"
    - "{{ ansible_os_family }}.yml"

# inspired by https://www.samdarwin.com/ansible-default-vars/
- name: Set facts while having include_vars variables have lower precedence
  set_fact:
    "{{ item.key }}": "{{ item.value|default(vars[item.key]) }}"
  with_dict: "{{ platformspec }}"

- name: debug
  debug: var=vars