get value from ‘terms’ table

get_terms does indeed fetch from the terms table, but it does also use a join on the taxonomy table, since you need to specify which taxonomies you want terms for in your get_terms query.

If you want to get all terms, you could use something like:

$all_terms = get_terms([
    'taxonomy' => get_taxonomies(),
    'hide_empty' => false,
]);