How many anointed were there in the first century?

The Watchtower study for 30 march to 5 april 2020 talks about the anointed and in paragraph 14 it says something interesting about the first century Christians.

The Watchtower says that in the first century all Christians were anointed. This is interesting because the place where we get the number 144.000 is in the book of Revelation. Revelation was written by the end of the first century. And according to scholars, by that time there were already around 500.000 Christians.

So if the Watchtower is correct and all first century Christians were anointed, there were already three and a half times as many anointed Christians as are needed by the time John wrote about the 144.000

Something does not add up. And it’s probably the assumption that in 2000 years God could only find on average 72 new anointed every years. That’s highly inefficient and wasteful.