Combine wp_users and wp_usermeta into a single table with columns (for wp_users) and a big JSON object (for all the wp_usermeta junk).

wp_users_plus_wp_usermeta.sql

SELECT
  u.id,
  u.user_login,
  concat('{ ' , group_concat(concat(m.meta_key, ': ''', m.meta_value, '''')) , ' }' ) AS meta 
FROM
  wp_users AS u 
  JOIN
    wp_usermeta AS m 
WHERE
  u.id = m.user_id 
GROUP BY
  u.id