Hold up: can we take a minute to talk about how painfully stupid the Iron Borne are? In order to see if their “Drowned God” has chosen someone to become king, they drown him in the ocean and then see if he comes back to life on his own. No CPR, no clap on the back to burp out some water, just good ol’ fashioned drowning and waiting.
In other words, every single king they’ve had has at least SOME brain damage.
No wonder they lose every rebellion.