Knowing, objectively, that there is more to be had, and an idea of how much more, is of great consequence in development. It's not for nothing that the cliche is "moves the goalposts." Where you aim is generally where you land. Ferrari knew after 2014 and early 2015 where they needed to work, and the effort has shown results.
I'm not saying that this is the only factor, just that it was a large advantage that Honda squandered.