It makes complete sense that Danaerys's drive for power would end up destroying the world instead of making it better, and that Jon's commitment to being "good" instead of seeking power for himself will prevent him from achieving happiness. Maybe he will kill Danaerys and prevent a reign of terror, but it wouldn't make sense for him to become the "good wise king who rules for fifty years" at the end of it.
I think looking to "Fire and Blood" is a good way to see what Martin thinks is the type of person who is the "ideal" ruler in this universe.
King Jahaerys Targaryen is the main standout in that regard.
From the wiki:
Jaehaerys I Targaryen, also known as the Conciliator, the Wise or the Old King, was the fourth Targaryen king to sit the Iron Throne. He ascended the throne in 48 AC following the death of his uncle, Maegor I Targaryen. Jaehaerys was the longest reigning Targaryen monarch, sitting on the throne for fifty-five years. He was a dragonrider, riding Vermithor, the largest dragon after Balerion and Vhagar.
Jaehaerys was wise beyond his years.[8][9] He was fair-spoken, open-handed, and as chivalrous as he was courageous.[10] According to Grand Maester Benifer Jaehaerys was "learned as a maester and pious as a septon". Although Benifer might have attempted to flatter Jaehaerys with such a statement, according to Archmaester Gyldayn there was some truth to it as well.[10] Queen Alyssa, Jaehaerys's mother, is reported to have called Jaehaerys "the best of my three sons".[10]
Jaehaerys was decisive in both thought and deed, and always sought the most peaceable ends.[8] In times of trouble, instead of brooding on the issues, Jaehaerys would shrug off his sorrows and plunge himself into his work.[11][5] He never acted without thinking,[12] and did not trust in chance.[4] Nor did Jaehaerys like to make outright threats, but had other ways of making his disapproval felt. According to the Sealord of Braavos, Jaehaerys was very skillful in making veiled threats.[5]
You can hear some things there that sounds a bit like Jon, but the main difference is that Jaeharys was all about
compromise. He was known as "The Conciliator." He was pragmatic. He was also proud and severe. He understood the need to command respect.
Whereas Jon is quiet and self-effacing to the point of being almost meek, in some ways. He makes no bones about the fact that he doesn't
want power.
Jahaerys knew he was destined to be king from birth. He was raised to the throne when he was still a child. From the beginning he acted like a person who had spent a lot of time thinking about the fact that he would be king. He embraced power, but seemed to recognize that the only way to keep it would be to not abuse it.
One way to put it might be that Jahaerys was always so secure in the knowledge of his own power that he didn't feel desperate to hoard it, flaunt it, or preemptively strike at those that might try to take it from him.
Jahaery's major defining actions were initially pardoning the lords that had sided with his predecessor, Maegor the cruel, and later undertaking to codify a set of laws to govern the entire seven kingdoms.
I'm not sure I see anybody in the current cast of characters who is really analogous to Jahaerys.