- Neutral creatures in Heroes 3

With an expert in diplomacy and a sufficiently strong army, thieves are not needed at all.

But here, I disagree with you... precisely because you have an expert in diplomacy, you want to see the attitude of the neutrals. And if there is no vision, then thieves become useful...
But still, the question is, how often do people (players) use thieves, and how often do they "ignore" them?