(Hero - Rogue) in Heroes 4

Actually, DeadDreams is partly right.
I remember playing with Chameleon about 4 years ago on "If these walls...". I was very unpleasantly surprised to find one day that I didn't have a capital city on the day of Creature Growth – a minor thief sneaked along the edge and stole my dwelling.

What prevents leaving some weak units in the city for 1k, if there is such a risk of a thief? Besides, on those same walls, it seems that fighters are valued more than monsters. That is, you can easily outsmart the monsters in the army.

In general, a thief is certainly useful, and you can get a lot of benefits from many units, but is it worth spending a week hiring a thief? Unless, after hiring the main forces, you use him for such raids.
I might not have understood DeadDreams's thesis correctly, but it seems that to collect artifacts, you still need to level up the thief to at least level 4 in stealth, otherwise you won't be able to collect artifacts properly.