I don't know why tptacek's comment is downvoted.
My take is that Enrique Allen, the guy behind the D-Fund, is not trying to say "startups should focus more on retention and user experience," he's trying to say "startups should think about users in an effective way."
In a recent talk Allen gave, the designer-founders he mentioned all had significant programming experience.
Almost all of the people he mentions could code their own products. So, he's not saying "get a bunch of photoshop designers to improve your ux," he saying "having people who think from a design perspective can be the difference between a product succeeding and failing."
For him, a design perspective could include something like thinking "how should I construct this API so that people will be able to use this library?"