I feel like I should mention that Sorcerers also choose their subclass at level 1. That makes a quarter of the twelve classes from the players handbook. Wizards and Druids choose their subclasses at level 2. The decision to unify subclass timing affects almost half of the original classes.
That said, I have to agree that the change really makes starting at level 3 seem intuitive for more experienced players. I wonder if the new Monster Manual will reflect that in the new monsters it provides.
As an aside, the mechanical change in subclass timing does not need to be reflected in storytelling. I personally wouldn't dream of making a level 1 character without knowing what subclass I was angling for later unless the DM suggested they wanted to choose for story reasons. A level 1 warlock can still have a deal with a devil, the deal just only starts looking different from other deals later. At least that's how I'd want to play it.
