The introduction of mercenaries in Diablo 4 is intended to compensate for the shortcomings of classes

Blizzard Studios commented on the goals of adding mercenaries to Diablo 4.

The characters that will appear in the game with the release of the Vessel of Hatred expansion will compensate for the shortcomings of certain classes. For example, Wizards, who are not able to absorb much damage, will be able to concentrate on magic, covering the back of a strong warrior. Warriors, on the contrary, will receive a damage dealer in addition, which will compensate for the lack of damage to enemies.

The release of Vessel of Hatred will take place very soon, on October 8.