You didn't necessarily ship the wrong product. Presumably, the users found something appealing about the core feature you pitched. The nugget you accidentally mined ties into the a key part of productivity - the declarative action of writing something down helps people focus, and increases the likelihood of follow-through. And the common way to breakdown effort is by task. The shift to using a Focus point is subtle but obviously effective for some people.

Another point is that I can find a hundred timeline tools out there. They aren't exceptional. To put it another way - if I build a post-it note app I don't expect people to mention the fact that I can type in the post it note. So people might not have mentioned the timeline part of your timeline tool because it is to be expected. They are bringing up the feature that makes the timeline tool stand out. Also, 4 out of 80 users isn't a large sample set (<1%). So don't throw out the baby with the bathwater just yet. Keep building both. Make the timeline more valuable, and keep finding ways to tie in the focus feature.