Narrow Runway
You forget one minor point: evryone here is naming the BBU allowance a "housing allowance". That is only part of the story.
To be completely fair in your assessment of BBU "privileges", we could compare how many sectors the Wizz pilots fly per month in Gdansk or Katowice. Every month is about 50 sectors or more. BBu has long night flights and longer sectors in general, many pilots don't exceed 30 sectors per month.
This allowance was taking this into account too.
Flex