This user is right. I was about to laugh at him and did some research:
– Baidu, the chinese government controlled search engine still uses meta keywords: meta-keyword-tag-a-factor-in-Baidu
– Yandex, the Russian search engine controlled by Poutine still uses keywords: google is not alone
So, yes, the keyword meta tag is still relevant if you live in Russia or China. If Yoast SEO doesn’t want to integrate these markets, that’s fine there are other plugins available ??