So how is this better play - everyone at the table knows what the situation is, but the players aren't allowed to act on it until they make a successful roll - than allowing the players to just make the choices they want to make from the start?Practically (in play) after the first round of attacks and only after some have hit (this is important), the DM could/should give the players a chance to roll an Intelligence check to figure out something with regards to the beast's vulnerability or they could just Say Yes and provide the information since the gotcha moment of the puzzle has been passed.
I mean, there isn't any "gotcha" moment if the players already know.