Shnurov overtook, answered for me :)

But sometimes on the map, you know in advance that playing with a certain castle is impossible without some luck and a specific set of circumstances.

Here it is, the key point. You knew that Barbarians were inherently weak on Iron. And Seaman knew something else. And he won ;)

For Barbarians, you could add a conservatory to level the playing field a bit.

Let's put it this way. How many times have you played Iron with Barbarians to say that they are weak there and need to be buffed? You need to buff when there is at least some data. Until then, all buffs will be a shot in the dark.

For example, Life was buffed on Iron only after many, many games with Life.