The challenge with this poll question is that it doesn't ask whether this issue changes a potential voter from someone who wouldn't have voted for Harris into someone who would have voted for Harris. It asks if they are more likely to vote for Harris.

For example, I was already highly likely to vote for Harris, but her being more emphatically against the genocide would still have made me even more likely to vote for her.

To make the case that she should have used this poll to change her position, you have to look at the pre-existing likelihood that someone would vote for her and see whether this issue brought them over that threshold. (For example, what fraction of the 35% voted in the primary and the midterm election? Were they already planning on voting? Who were they planning on voting for if not Harris?)