The first paragraph is how I imagine he was during the first few centuries of his life, when all the scars were fresh and he had no idea how to deal with it. From the sounds of it he has been in ruling positions, and may have even enjoyed it briefly, before he adopted the humble mindset that he has now and tries to inspire humanity with small acts of compassion.

(I write "adopted" but I like to think that his actions actually reflect the hazy consciousness of humanity at the time, and so maybe he was molded into this persona over the years, as humanity grew somewhat kinder? Or he learned that the highest value one can have is not through wealth or power, but through compassion, i.e. something that all humans would eventually learn, a.k.a humanity does have value if given a chance).

I do wonder how his skills have decayed. Can he juggle? Can he do a backflip, or it's been too long and he no longer remembers how? How elastic is his brain exactly, and what precisely is there left of him in there that just isn't a hazy imprint of his circumstances over the last few centuries.

Imagine a neural net with limited nodes that has been subject to more training data than it can handle. Eventually it just learns to approximate all the data it has seen (overtrained) and isn't elastic enough to predict or react to new stimulus, and becomes set in its ways. Is this the case with John? Or does he summarize old historical data and leaves himself with enough elasticity to learn new things from the last X decades?

Yes and No. You could argue that True Love was the factor between them