The majority of his killings weren't by arrests.
The great purge killed around 681,692 people, mostly political rivals obviously like Trotskyists when Stalin found out Yezkov had been killing some people for his purposes, not Stalin's, Yezkov was killed off too.
The Soviet famines killed 7.5 million in Ukraine and between 1 and 2 million people died in Kazakhstan and around thousands in the Caucasus and Southern Russia. So he killed around 8-9 million people (not 60 million) I'm no fan of Stalin but it simply isn't possible to kill 50% of your own country whether you are Stalin or not.
The purpose of these famines was called by Lenin as ''food dictatorship'' it would lead to a great exodus of young people from Soviet farmlands to migrate to big cities like Moscow, that was part of his plan to industrialize the USSR he needed those young workers, and the old ones died in the famine.