a) absolutely damning! SBF's lack of empathy, his notion that (given that everyone else is stupid) he knew best and should basically ignore the advice of everyone else (particularly his elders), his naive utilitarianism without any deontological/virtue temperance, his reckless "many-worlds" risk-neutrality in gambling - that was all described in detail in the book, even if it was not explicitly condemned. Lewis didn't bother to show why these traits are bad. (I don't know what Lewis himself thought about them, but who cares? Show, don't tell.)
b) empathetic, eliciting compassion. Sure, the kid was screwed up, but here's why. And, btw, you might well have turned out the same way under similar circumstances, but for the grace of god.
My conclusion: 1) Lewis's book was good and insightful, and it's unfair to describe it as an apologia. 2) SBF has severe moral deficiencies and belongs in prison for a long time, but not because he is "evil". 3) Let's have some damn humility.