World Championship in Heroes of Might and Magic III.

I wrote it this way precisely because I've encountered similar situations generated in my maps multiple times. Even in "hotseat" games. Generation after a Castle – guarding a nest of Angels, an Horde of Mummies – I took it on the first turn. Also, it's easy to break Griffins, Demons, and Pit Fiends with ranged attacks (it will be more difficult for Swamp, though), up to 10 creatures of level 6, sometimes even 10+ Manticores, Vivs, and Nags, etc.

Wistan will tear all of this apart and, with an equal number of stacks, will not be inferior to Valesk in any way. Also, Swamp can quickly create 3 decent stacks for a quick attack and defense – Ducks, Cows, and Basilisks (and they will be targeted less due to their defense), while Castle will get at best 2 Knights with 115-116 attack. Blocks that are more difficult for Swamp than for Castle are practically impossible. Even if Castle breaks through the first guard of the Hive, there is practically nothing for it to do there, unlike Swamp. So, everything you said is, to put it mildly, very, very debatable. In general, all the troops in Castle are much weaker than in Swamp, and that's a fact.