This is one of the well-known ways of pumping. Kurak, Al-Meriah, The Purge.
In this case, through killing golems during Purge of 6-8 levels.
I just want to note that fast leveling up to level 20 does not allow the slave to eat the food necessary to increase the probability. Thus, pumping truly elite thralls through Purge is not recommended.
At the same time, you can put pumping on stream and then select the best thralls.
For example, arrows made of star metal. (О_О)
3 golems are enough.