Am I cheating by already having a list of things to study and a large collection of papers to read?

Not really, but only because the example you gave was Astronomy. If we're talking specifically about Existentialism (although I guess the conversation has progressed a bit passed that) I'm not entirely sure how one would come up with a list of readings and concepts without turning to the writings of the Central Figures (I'm not even sure it's legitimate to call Camus an 'early' thinker, since the Golden Age of Existentialism was definitely when he and Sartre were publishing.)

I would very much agree with your assessment for many if not most scientific fields, but in this particular instance, I happen to disagree that disregarding the Central Figures won't hurt your knowledge and understanding of the topic.