Character arcs provide the skeleton, but development gives it flesh. I've read too many books where a protagonist ticks all the classic 'Hero's Journey' boxes—they start here, they end there, they learned a lesson—and I'm left completely cold. It's like watching a robot complete a checklist. The actual change felt mandatory, not earned through the tiny, cumulative moments that make a person feel real. That's where development lives: in the specific, often quiet choices, the hesitations, the minor hypocrisies, the small kindnesses that contradict their stated goal. An arc is the destination on a map; development is the texture of the road, the weather, the blisters, and the unexpected detours that actually transform the traveler.
I'd take a story with profound, believable development and a subtle, ambiguous arc over a story with a perfectly symmetrical, obvious arc built from cardboard character changes any day. A character can have a massive, world-altering arc yet remain a static personality. Conversely, a character whose worldview doesn't radically flip can still undergo immense internal development, deepening in their convictions or understanding their own flaws more intimately. The latter is often harder to write and, for me, infinitely more rewarding to read. Give me the messy, incremental growth over the neat, predetermined transformation.