Onassis proposed two customization directions: one was to refine a weapon; the other was to refine any item related to philosophy.
Angel chose the second customization direction.
Not because he was particularly passionate about "philosophy," but solely because Onassis had suggested too many paradoxical requirements for the weapon—things like "a radiant black," "must be both restrained and grand," "sharp yet with a touch of smoothness," etc. Compared to Onassis's requests, the second option seemed a much simpler task.
Though Antonio had said there was no need to heed these unreasonable demands, given that this was a customization for the champion of the Nova Competition, any serious attempt at refining would need to consider a bit more.
Angel simply didn't want to waste time and effort researching Onassis's contradictory demands for the weapon, so he chose the second option.