Gaim's ''formula'': A story that begins with a casual and childish use of supernatural powers and
slightly friendly rivals. Life is fine.
Then it turns out that what they were doing doomed many of them and was part of an even bigger doom.
All of them change, whether they grow up to become stronger individuals or get more evil and twisted as time passes.
Multiple Riders. Multiple users of similar belts.
Other than the multi-Rider part, this is not really a formula because it hasn't been repeated yet. There's probably even more I'm missing.
Having more than 5 Riders in that show fighting each other it's something that has happened before, and the episodes in which they were introduced might seem like a formula.
Imagine the next series does this: 7 Riders are introduced in the first 10 episodes, a few of them have multiple forms. Beginning around episode 12 new Riders are introduced, with upgraded systems and weapons. From there, only new forms are introduced, mostly for the main Rider.
Gaim did not break the formula of the ultimate form, by which I mean the time it takes for it to appear... or there being an ultimate form in the first place.
The point is, there ARE things that could be repeated. But they shouldn't be called a formula.
It was slightly different in that there were multiple Riders towards the end of the show while the others (and Den-O) only ever had two
If you mean having 2 new Riders only, I'd say that should be attributed to Den-O more than W.