I was thinking about some accusations here that the captain didn't call "Brace!" for the passengers, and here is the result of my mental effort.
I don't think a call to brace would help anyone. Even in the most airborne country like the US, most passengers would simply not understand it. Other than a few aviation enthusiasts, very few people actually know what this word stands for. They've just boarded the plane, they are tired from all the lines they had to stand in, they are utterly irritated by their encounter with the security, they are finally trying to relax. The plane accelerates down the runway, the shaking stops, and we fly, and the suddenly "BRACE! BRACE! BRACE!"... What do you do? Hug a person in the adjacent seat? Grab the armrests? I don't think it'd work, especially with panic factored in. Even people who know the meaning would need time to process the command, and those who don't know would simply wonder what the heck the PA is screaming about.
And now imagine there is a plane full of people who don't speak a word in English, and there is no set phrase in their language for "assume the brace position". Heck, I just realized I don't know that phrase in my native language, and those that I can come up with would require quite a few seconds to say.
So, in my conclusion, "brace" command, unless called well in advance, gives absolutely NO meaningful result and doesn't improve the outcome by one iota.