All castles in Heroes 3.

In my opinion (but not in the provided explanation), they are actually the weakest races in the game. Although, Conflux has good mage heroes.
But why attack him? His units don't deal much damage, they are vulnerable to magic, and he only has psychic elementals.
And Necromancers have too weak units. Only Vampires and Knights. And Dragons are a joke.
Maybe you can explain what makes them overpowered:confused:

NECROMANCER:

a) Skeletons are weak, but there are many of them (if there are few, then the player is just bad).
b) After building Liches, the number of skeletons ONLY INCREASES (again, if this is not the case, see the previous note).
c) You can't call a Lich weak - it's generally the second-best ranged unit among neutrals, after Titans, which I only risk attacking in extreme cases. And to prevent them from being defeated in melee combat, you need to protect them!
d) Magic won't help much here. Mana is not infinite, and powerful spells are expensive (Explosion - 25 units with an Earth Magic expert skill of %( ).
e) Even after fleeing the battlefield after a battle, the opponent strengthens the Necromancer by increasing the number of skeletons (although the upgrade doesn't change). For example, with Iskra at high levels, the skeleton output tends to be 80-100%.
10% for Necromancy amplifier + 30% for Necromancy expert + 20*0.05*30=30% (per level) + 10-15% from artifacts (there is at least one on the map) = 80-85%

CONFLUX:

a) Huge increase in creatures (about 30 Storm and Ice elementals).
b) Tremendous speed compared to creatures of a similar level. Phoenix is generally the fastest creature in HOMM3.
c) Frequent random drops of magic school upgrades for heroes - many have them initially.
d) The Sprite in blue is a unique unit for the beginning of the game. With an increase of 40-50 (I mean the beginning - the castle is not given immediately :) ), cheapness (including the upgrade), and coming with heroes (there are usually about 20-30 sprites in red), it easily defeats neutral stacks of levels 1-2, including Orcs, by using the tactic of waiting, attacking without response, and retreating. The hero goes to gain experience, having only sprites and a magic arrow, and the castle is being built, and the number of creatures in it is steadily increasing...
e) Phoenixes are cheap and relatively quickly built - mainly mercury is needed.

In conclusion, I would say that it is better to play as Necromancer on XL maps - there is a lot of meat, and opponents are usually far away, and Conflux is for a faster start.
Everything written is based on the results of playing on the highest difficulty with a shortage of money and resources. Without this shortage, Elves are the strongest (somehow, there are always a lot of them ;) ). And I just like the Swamp - it's not weak, but specific - it allows you to enhance the sensations from the game!