You disagree with the idea that living unreservedly implies faith in God for you, but living unreservedly was faith for Bonhoeffer. There is no expectation that you need to adopt his view. Isn't this reasonable?
So the "we" he frequently refers to is the "royal we"?
The words "for me" don't appear anywhere in the passage you quoted. He's structured his argument as conclusions drawn from an assessment of apparent facts:
By this-worldliness I mean living unreservedly in life's duties, problems, successes and failures. In so doing we throw ourselves completely into the arms of God, taking seriously, not our own sufferings, but those of God in the world.
This could be re-worded as saying
"living unreservedly necessarily implies trusting one's life to God." It relies entirely on general statements, so the only way it can be true in any sense is if it's true generally. IOW, it can't be "true for Bonhoffer" unless it's true for everyone.
OTOH, something that is true generally is true for every specific case it applies to, so if it's
not true for me, then it's not true generally.
This brings us to a contradiction unless we modify the statement so that it's worded in subjective terms... but this would be a change from how you originally presented it to us.
Of course your view is welcome. What is faith for you, 9/10ths?
As I said earlier in the thread, I'd say that the term "faith" properly applies to intellectual assent, trust and loyalty, however, I think that they're all distinct concepts, and there's a tendency by some people to falsely equivocate between them.