This is a pretty crass statement to make. If the focus is full-on navigability, I agree that contrast in the navigation bar is paramount. Yet, for many sites with simplified features, the emotional experience trumps the direct navigability of the site itself. This is especially true for sites like Airbnb (as in the example) where in addition to emotional response, there is an immediate focus on activating users. The…
"...the emotional experience trumps the direct navigability of the site itself" The above statement is everything that is wrong with modern visual styling of software. After everything is said and done, software is a tool which people use to accomplish a goal. I would argue that anything that causes friction with that is Bad Design. As much as some visual/interaction designers may think that "experience is everything…
Basically, within a given flow (say onboarding or signup), you want to consider having some points of friction interspersed with low friction points. Adding friction in the right places helps to create users who will a)come back and b)will be more active users. The speaker presented some data to back up her assertions.
Getting back to OP's point, the emotional experience is a point of friction that may be worthwhile. Though it may slow down the conversion process or whatever flow the user is supposed to go through, it may result in users who become more attached to the product and ultimately spend more.