The most “remorse” I remember him feeling was for killing Cassius’ brother (whatever his name is), but then it felt more like he was just afraid of Cassius than feeling sorry. I wouldn’t really have an issue with him murdering people left and right if it was played as the “you become the monsters you battle” trope, I don’t know, it may be just that in the other books, I haven’t read them. But I doubt it since

In the first book to me it came across as a simple power fantasy.

It left the same impression on me. A friend recommended it to me and he was insisting that I’d love this trilogy. Maybe it was this that set up a high expectation, but I didn’t enjoy it very much. Actually I forced myself to finish the first book, I don’t know if I will finish the trilogy. I felt like the main character was driven by the plot instead of driving the plot forward plus an occasional power fantasy moment. And most of his character development was hidden behind the book equivalent of the “training monrage”. I saw a little change from the beginning of the game/competition (or whatever they called it in the book) forward.