It's hard to say that the car was designed around Neuville. Ofcourse he had an advantage vs Ogier going into the Fiesta blind, but Thierry was the last Hyundai driver to test the i20 because he took a while to commit his future to the team in 2016. Abbring, Sordo and Paddon etc all had tests before Hyundai let Neuville drive it. It's not like they designed the car specifically for Neuville when he potentially could've moved away.
The i20 definitely seemed the fastest car in the early part of the season, Neuville just blew two comfortable leads in Monte and Sweden. The fiesta was very good and had a wide operating window, but it wasn't the best car out of the blocks imo.