Of the traitors I ways had sympathy for Fulgrim, and the novel was fantastic imho.
Fulgrim tried so hard, tried to be all that was perfect and it was this push for perfection that lead to his downfall, to which in itself is a great warning about striving for perfection.

Magnus was unfortunate, he fell for the Emperors lie and paid a huge price, Fulgrim and Horus are also victims of this.

Who knows what A/O really want or believe, the legion was made to be special ops and if not somehow renegade would be the ideal chapter.