The Johto saga technically isn't, the "early years."
It was the whole second generation. Classic Pokemon ended with Orange Islands at the latest.
Yet more often than not people include Johto along with Kanto and Orange islands as classic era of pokemon.
Which is probably because of original trio, older pokemon from Ash being largely present taking away focus from JOhto pokemon etc.
But the problem is Johto was long and still nobody really developed. Ash's Johto team didn't go through much development at all. I still can't believe Ash only had one evolution over the entire 150 ep span of Johto.
Im not sure how "no one developed"?
Ash became abit more mature and strategic in pokemon battles which can be noticed during Johto gym battles and battles in general not being so brash, naive and hotheaded like we used to see him in Kanto, OI days. We also saw some of pokemon like Bayleef growing as well realizing she became too heavy to jump in Ash lap and became less infatuating after evolution.
Misty became more mature and levelheaded growing to appreciate her friendship with Ash and Brock , improved as trainer and got over complex of feeling inferior compared to sisters. Growth which was further carried to chronicles and specials after departure becoming more responsible and confident in herself and abilities as trainer. We had quite a few episodes focusing on her growth like "For Crying Out Loud", Whirl cup arc, "Some Like it Hot" etc.
We saw Brock enriching his knowledge as breeder learning about new medicines and potions applying his knowledge on several occasions. Such as taking care of young Stantler, entering breeder contest with Suzie etc.
To extent we can say Gary grew a bit too becoming more calm deciding what he wants to do with life.
Admittedly gaps between moments where characters or pokemon experienced some form of growth were big often filled with episodes of no importance, which i guess made such things less memorable.
But yes in Johto there existed development, even though it wasn't done on daily basis not being treated as coherent story telling.