The client did not accept the change referring to the fact that iOS widely uses this practice already. You definitely can relate to this, but I thought it might be useful to gather some arguments to lay out in the next conversation.
One Field Is Perceived Better than Two
The purpose of any system signup or registration is collecting the necessary information about a user. Nobody likes filling in the forms. I mean, remember filling taxation papers or some bank documents. Any form is a serious challenge for a user and the amount of fields is a powerful influential factor.
The more fields, the more chances to go wrong and make a mistake. Making a mistake results in an unfinished signup and frustration.
The UI has to adjust to the needs of a user, not the other way. Fifteen years ago the algorithms were not profound enough to figure out how to separate the fields the right way, so the decision was passed on to users.
If the interface is to be used by people of different countries, a lot of users might encounter difficulties as different cultures have various traditions of recording names, which can be outside of the first name & last name paradigm.
With European naming standards being natively accepted in UIs, it took quite some time to redefine that policy and start thinking outside of the box (pardon the pun). This had to deal with global development trends and international expansion of technology.
In the modern world there is no place for rigid formalities and functional rationality along with appeal come into play more and more. We create experience and navigate affect, so let’s consider the intricacies as well!