I'm not sure what you'd find preferable. Battler discovered the truth, yes, and he didn't think it was worth sharing. That's not hiding from the truth; quite the contrary, he was taking all the responsibility for knowing it onto himself. He wasn't hiding from the truth, he was just hiding the truth.
I'd find it preferable if Battler didn't lie to his little sister the same way Beato lied to him at the start of the series. Implied in the search for truth is the idea that it's better to face reality than swaddle yourself in fantasy. By denying Ange the truth, Battler rejects that proposition.
--
another place and time, without a great divide, and we could be flying deadly high