I often think I am alone in thinking of David as not being the most impressive hero in this novel. Let me explain and justify my viewpoint. If we consider the story, which is of course told from David's point of view, it becomes clear that David is certainly not a character with natural leadership abilities, as the way in which Michael assumes leadership of the group demonstrates. In addition, he is not necessarily quick thinking and resourceful, and relies on Rosalind to prepare them for their flight. This is demonstrated when David spends the night before their flight sleeping whereas Rosalind spent it busily packing and preparing:
And so when I tried to consult you about it, there you were, swinishly asleep. My mother and I spent two solid hours packing up these panniers and getting the saddles slung up ready for an emergency, while all you did was go on sleeping.
David hardly seems to be able to act to ensure his survival by himself, as this example demonstrates. Throughout the novel, he remains a passive figure, who seems to just report what is going on around him rather than seeking to make a change and have influence himself.
If we think about his strengths, we see that his primary strength is his ability to empathise with others, as is shown through his first encounter with Sophie. Note how he interacts with Sophie's mother in the first chapter after discovering Sophie's extra toe:
I could feel her anxiety strongly; though quite why she should be so worried was not, at first clear to me.
David, because of his telapathic abilities, is able to tune in to other people's emotions and is sensitive to their feelings. This is a definite strength, however, as I argue above, I don't find David an impressive hero in this story at all.