This city is much like a little hub in its own right. When you arrive at first, there is a roadblock to the south that denies you access to Route 32, and you must obtain Violet's gym badge to pass. However, the surrounding points of interest, namely Dark Cave, Sprout Tower and the Ruins of Alph can be freely explored at your own leisure, or perhaps not at all if that's how you feel like approaching the game. Violet is the centerpiece that ties each of these landmarks together.

This is the correct way to design the campaign progression in Pokémon. One roadblock, one path of critical content, and numerous bits and bobs to do and see in a somewhat contained area. That is how you make the game non-linear without making it open world.

In the modern games, progression is more waypoint-based than not. You often simply go from Point A to Point B, usually with a character that holds your hand along the way. Whereas if Violet City can be considered Point A, then Dark Cave is Point A-2, Sprout Tower is A-3, and Ruins of Alph are A-4. Point B isn't truly anything but Azalea Town.