There is no basis for your statement that "the risk of recidivism seems quite low".On what basis?
I don't follow, because he has not "suffered" in other ways, prior to his offense, he should be subject to the prison system for all its shortcomings that you reference? I don't think this reflects Timpson's views at all.
In fact, it seems to me to be entirely opposite. The risk of recidivism seems quite low in this case. I don't see how society would be safer with him behind bars? It seems a far greater risk to society is to place what was a seemingly functional member of society, into a system that can only disimprove his social functioning the longer he is in it.
Quite just as easily argue, if he got away with one such attack without any real consequence, it would be a signal to him he could get away with others.
The consequences should involved time behind bars.