What Jean did was something no one thought could be done. It is just a legend in Time Lords Records
Changing not one moment, nor one choice, but to delete it all and start all over again.
The energy needed to orchestrate such changing of destiny and fate is incalculable.
But he did it.
He did it and now the entire time and space, the fate and destiny of everyone had changed slightly.
And that slightly has become more and more obvious , more and more prominent. As for him?
The moment he regain the memory of that deleted timeline, he did what he should have done in the past.
Righting the wrong of his past self.
All the regrets, all the mistake, all the things that should have a solution. And because of this, he is also considered a renegade
Because a Time Lord should not mess with time. At least not to this extent. What Jean had done is a horror to many Time Lords
I think Qarthans were mentioned in the very first chapter. They are also mentioned a few times but never was truly expanded