Is Stealth actually that useful in Heroes IV?

From my experience, Stealth is a very powerful tool on L and XL maps.

1. You can steal resources from stacks that you cannot beat yet, it's important if your map has powerful monsters.
2. After some time XP gained from sneaking (in addition to XP gained from battles) exceeds the XP that you had to spend on Stealth, so you have extra skills in late game
3. After all, you got Pathfinding and Scouting, you do more things in one turn!
4. You can sneak past enemy players and, for example, ninjacap their city, dwellings, and other objects. And if they didn't develop Scouting 5, they will have a hard time finding your hero in their ranks.
5. At the same time, as far as you don't actually need army, especially after your Stealth hero also develops Combat 5/MR 5 and some kind of magic. You can give your army to other heroes.
6. If you have a group of heroes leveled this way wandering together, you will actually get even more power. Yes, they will all be of lower level than one single hero, but they will have a bigger total of Skill points due to exponentially growing XP requirements for each subsequent level, and, more importantly, make more actions per move. What's even better, someone playing L or XL maps against Chaos might expect a sudden sneak attack, but not from 7 heroes at a time.

But I noticed that this skill is overlooked and considered weak at Heroes IV forums. Also noticed that maps discussed are typically of M size, because playing an L/XL map would take too much real time. By no means can it work on S and M maps, this scheme takes time to perform.

Is there something wrong with this skill that I don't understand? Do other choices outperform Stealth focus even at L/XL maps?