The Hero's Path

Initially, it was indeed intended that players could choose a class, but the game has a very fragile balance. Necromancers are overpowered due to their ability to raise undead; mages gain all spells from their super ability; Barbarians and Dwarves are tailored to their specific troop types. The Warlock would conflict with the ability to purchase enhanced Chaos spells. In short, this feature is not currently planned. Moreover, you can customize a hero's skill set to play as either a warrior or a mage.

You can't raise a large number of undead with a single hero without a castle – the weekly limit won't allow it. A Necromancer wouldn't kill one unit at a time each week just to raise them; they wouldn't progress, and would actually fall behind in development (although the map allows for a leisurely playstyle, which I really like).
Gaining all spells also seems to me to be nothing more than a way to save money – everything interesting can be purchased here, and perhaps even earlier than the hero reaches the level required to gain the super ability.
Barbarians and Dwarves are indeed tailored to their troops, but their troops can be easily purchased in the corresponding camps (although, in principle, they could be excluded from the list of available classes due to their specificity and connection to the race).
As for the Warlock, what conflict are we talking about? The class ability simply allows them to obtain enhanced versions of spells for free if they have the basic versions – that is, again, it allows them to save money in exchange for an occupied perk slot.
I initially suggested this precisely because the ability to play, for example, a Chaos mage is very limited: unlike a warrior, they have nothing to buff themselves with before battle, as neither potions nor runic magic provide a bonus to spellcasting, and the Knight class is very poorly suited to this playstyle due to the lack of talents such as spell luck and resistance penetration.
Overall, it seems to me that if such a feature exists, it would be better to implement it – it would take the game to a qualitatively new level.