The pitch most pitchers are missing isn't their nastiest one. It's the boring one in the middle.
Here's how I build an arsenal that actually works:
Three pitches. Three speeds. Three movement shapes. All coming out of the same tunnel.
Up-and-down: fastball, gyro slider, curveball.
Lateral: sinker, cutter, sweeper.
Fast, mid-speed, slow.
The middle pitch is the anchor. Most guys skip it. That's the mistake.
Reason one: the smaller the movement, the easier it is to throw for a strike. So in fastball counts, when I need the zone, I throw the mid-speed pitch. High strike percentage, and it tunnels with the fastball. The hitter sees the same window out of my hand and has no idea what's coming. He's guessing on speed alone. That's where pitchers win.
Reason two: once that middle pitch is doing its job, I never have to throw my curveball or sweeper for a strike. I save the big breaker for two-strike counts, for chase situations, for the moments when missing the zone is actually the right play.
A fastball and a breaking ball is just two pitches. Add the middle pitch and you have an arsenal.
Most pitchers are one pitch away from being almost unhittable. They just keep looking for something nastier when the answer is something simpler.