With the health bonus, there was quite a story – in the fixed maps, everyone played as mages, so Horn, during the development of the Town Enhancement, strengthened warriors and weakened mages. The health bonus was invented precisely for this.
In random maps, the task is reversed – to strengthen mages and weaken warriors. Therefore, the health bonus can be removed; it doesn't add much in terms of strategy. Heroes like Shahti, Galtran, or Taras will be perfectly fine without the bonus, and other heroes will have a better chance of becoming powerful.