That's an interesting way to think of it. But I do feel like you're over-generalizing the Cell Saga.
It was never about training and fighting etc. The whole arc had this domino effect created by everyone's mistakes within the said arc. I could start from their failure to destroy Gero but I'll just go off based on the appearance of Cell. Piccolo letting Cell get away, 17 not running away, Vegeta being overly confident in his power leading to Cell attaining Perfect Form, alongside Krillin's Reluctance to blow up Android 18. Gohan becoming over-confident, thinking he can beat Cell with his new-found power, leading to Goku having to sacrifice himself and Gohan injuring his arm trying to protect Vegeta.
When it comes to power-ups, I'm pretty sure they developed it quite well, with Goku having the idea of perfecting the super saiyan form. It was never about finding a new form, rather perfecting the power they already came to achieve. It was Gohan's Potential that led to Goku thinking of the possiblity of a New Form beyond Super Saiyan. The evidence of that can be seen in the Super Vegeta and Super Trunks form, which then eventually led to the hint of Super Saiyan 2 when Gohan powered up in the Time Chamber.
Majin Buu Saga did create that issue of new enemy, new form, new power-up, but even then that was only for Super Saiyan 3. The Arc built on newer fighters like Goten and Trunks as well Gohan becoming the defenders of Earth, and Goku only intervening to fix their mistakes. They never used a new form to defeat Kid Buu, it was the combined powers of all the earthlings.
There seems to always be an over-generalization for Dragonball Z's writing, but that isn't really the case. DBZ has very deep writing but people do tend to have this idea that it's just Good Guy fight Strong Bad Guy, Good Guy get power up and Win.
