Life Buildings

I agree about the hero, but on many online maps of sizes S and M (for a player versus a human opponent), there is an additional castle and two more additional castles.
Examples: heartwinter, If These Walls Could Talk, showdown.

We both understand this perfectly, and I think that having two castles and building different units there is complete idiocy.

They can be easily contained by any army due to the terrain.

If the opponent is an AI, then yes. But otherwise, it will be difficult... there are rarely many natural obstacles on the battlefield, especially a player who has brought champions to the battle will carefully protect them and avoid logs/stones and other nonsense... so it all depends on the skill level of the players, again ;) Moreover, champions are usually placed in the front line.