For some reason, according to your logic, Valeska should always start with 10 units – it seems strange. And adding 10 more units to the second starting hero increases the number of units from 24 to 50+ :D
In reality, Valeska with 13 marks and 24 units will defeat far more demons than, for example, Sorcha with 34 units and 4 swordsmen. Do you have any doubts? ;)
You also didn't understand – the option without archers is risky, tedious, and not very effective.
I always get at least 13 units with Valeska.
Nothing scares you about starting as Dess in Stronghold. It will be much harder to manage with only goblins than with pikemen. Does that make sense?