MySQL GROUP BY slows down query x1000 times

Is main_article_of_duplicate_group a true/false flag?

If the Optimizer chooses to start with newsarticle_topics:

 newsarticle_topics:  INDEX(newstopic_id, newsarticle_id)
 newsarticle:  INDEX(newsarticle_id, online,
                     main_article_of_duplicate_group, date_published)

If newsarticle_topics is a many-to-many mapping table, get rid of id and make the PRIMARY KEY be that pair, plus a secondary index in the opposite direction. More discussion: http://mysql.rjweb.org/doc.php/index_cookbook_mysql#many_to_many_mapping_table

If the Optimizer chooses to start with newsarticle (which seems more likely):

 newsarticle_topics:  INDEX(newsarticle_id, newstopic_id)
 newsarticle:  INDEX(online, main_article_of_duplicate_group, date_published)

Meanwhile, newsarticlefeedback needs this, in the order given:

INDEX(news_id_id, user_id_id, created_date, isrelevant)

Instead of

    COUNT(`newsarticlefeedback`.`id`) AS `count_nonrelevent`,
    LEFT OUTER JOIN  `newsarticlefeedback`
          ON (`newsarticle`.`id` = `newsarticlefeedback`.`news_id_id`)

have

    ( SELECT COUNT(*) FROM newsarticlefeedback
          WHERE `newsarticle`.`id` = `newsarticlefeedback`.`news_id_id`
    ) AS `count_nonrelevent`,