How to log outcome from multiple hosts in Ansible?
This question has two approaches, and both has answers on SO:


Convert all Ansible output to JSON with json stdout callback and parse it with your favourite tools. The eos_command output for each device will be under different host key in the resulting json.
See this and this.
Make run_once task to collect data from other hosts, like this:

- debug:
    msg: "{{ ansible_play_hosts | map('extract', hostvars, 'result') | map(attribute='stdout_lines') | list }}"
  run_once: yes


See this.