This is an example of the writers writing a twist just to for the sake of stirring drama, but without thinking of long term ramifications. Having it revealed that Hook killed Robert minutes after David gives him his blessing to propose to Emma was too juicy for the writers to pass up, but we all know they’re not going to have a good payoff. This hearkens back to the twist that Regina killed Marian in the original timeline. Unneeded and messy drama for the sake of drama. Emma and Hook are still going to get together, and the past will be in the past. It’s just another temporary roadblock, as far as the writers are concerned.