I've always had mixed feelings about him. In theory, everything looks great – you wander around, gain experience, capture mines and resources, and it's all wonderful. But in reality, it's incredibly difficult to level up his stealth. You have to sacrifice all the chests you find because he can barely reach level 2 by shooting at archers or fairies. This has a negative impact on the main hero or the economy, depending on the difficulty level. And you can't even rush through them. Plus, chests are limited, and they are often guarded by creatures above level 1. On top of that, you also need to level up scouting for stealth, and there's another skill in a different branch. So, in practice, by the time you level up the thief, you might already have a powerful creature. This is true for a typical map. But maybe if you play on a large, super-rich map with ten chests before the castle, the thief might actually be useful.