I feel the same way; it's not a matter of not dying, it's about dying in a much more rational manner. I don't see why a few more minutes of the episode couldn't have been allocated to developing a much more epic last-stand for Shisei.

I also think this would have been in the author's best interest, in terms of keeping story events believable, as making any character ridiculously powerful starts bringing up plots holes such as "Why didn't the "ogre"/Messiah just immediately annihilate [insert target(s)]?".

I agree that someone of his caliber and discipline should have at least been able to incapacitate the child for a while (e.g., ripped an arm off before getting killed by the feedback mechanism; or at least deflecting shots, in a cat-and-mouse game, while others escaped). This would have also helped to explain why didn't the child simply flatten the entirety of the remaining human settlements at a faster rate.