Is it necessary for a protagonist to continually gain power/ability/expertise as a series progresses?
For my book it's imperative the protagonist, at a bare minimum, grows emotionally. They can grow, break, and rebuild over the course of the series. The "break and rebuild" is useful if a series that was intended to be seven books suddenly becomes wildly popular with enough demand to justify continuing the series (hey, I'm allowed to dream, right?). However, if there's no character development internally and/or externally, then the series is Same Shit, Different Monster. That's no fun for me to write. If it's no fun for me to write, then it's no fun for anyone to read.
Regular visitors to this blog know I'm a planner. I plan the series arc and how many books will be in the series before I begin Book One. By having a predetermined end of the series, I avoid giving my protagonist too much power too quickly, thus robbing her of risks and challenges, which deny her character growth and make the story dull.
It is absolutely possible to over-develop a protagonist and have them grow too much too fast. Average Joan leveling up to an omnipotent undefeatable world-creator overnight is a trap that happens often in series that aren't pre-planned. The character has no space to grow. They have no believable opposition. They have all the gizmos, all the magics, all the knowledge...and the character fizzles. They're no longer compelling. Readers become bored and abandon the series.
Yes, there are series with 25+ books holding firmly in the Best Seller lists that have zero character growth. The books are as formulaic as the characters. Obviously, those stories aren't character-driven. Obviously, the audience for those books enjoys the comfort of predictability. Obviously, I'm not dunking on a dedicated fanbase for liking a style that's not mine. It's one of many reasons why there are few hard and fast rules in writing. Most everything is recommendations based on "what works for me. YMMV."
For me, my protags have to evolve over the course of a book and a series. Otherwise, what's the point of the story?
