Were the ox clan really stupid? No, they weren't stupid at all. Their cultivation talents were actually very good, but they were a little one-track minded. Whatever they did, they would always follow the same path. For them, this was an advantage and also a weakness.
It was an advantage because they had a high chance of success if they did so. Even if the path was wrong, they might still succeed in the end because they would keep discovering their mistakes and find the reason for their failure from their mistakes.
His weakness was that after they embarked on one path, they might not find other paths. Perhaps in their eyes, there was only one path.