Please explain.
In my opinion, it's not a very good Castle.

There's a separate thread on this topic.
It's better to ask Ta Kotoraya. I think she can explain it better.
Seriously, the downside of Necropolis is the lack of enough creatures to replenish its ranks. Conflux has almost complete immunity to life drain, and the Tower has Gargoyles and Golems; there are many of them, they are not very weak, and they can cause trouble...
Conflux is a great Castle, but not against the Tower. They have fewer archers, and they are weaker than the "Gremlin-Mage-Titans" trio.
But the main thing is that, with sufficient development time (we're not considering rushing for now), Mages have access to more 4th and 5th level spells... this is a significant advantage! With Dimension Door and Explosion (if the opponent doesn't have it), the player gains such an advantage that neither a horde of skeletons nor a large number of Phoenixes can overcome... and the probability of such spells appearing in the Tower is obviously twice as high as in other factions...
Besides, when playing as a Mage hero in the Tower, there is a high chance of getting Diplomacy. Can you imagine what a hero with Expert Diplomacy and Dimension Door (or Flight?) can do? ...just fly around the map and recruit friendly (or unfriendly but useful) creatures... the Clairvoyance spell can also appear more often due to the library.
I've already mentioned something about Necropolis: they appear in the Dungeon if it exists on the map. And in the Dungeon, the respawn is usually worse, and the paths are more confusing... which is not very good.
Here's a short explanation