I felt that the author was being pushed by his own 21st century beliefs into his shaping of John Smith, and that caused him to lose the plot.

I think it would have been entirely reasonable to have a 1913 schoolmaster character be prepared to give up his life to protect people, or to have him admirably realise that a do-or-die defence wasn't working and organise a planned retreat.

The problem is, he doesn't behave like a 1913 schoolmaster at all. He just seems panicky and confused.