To verify and prove that you have a new, original thought, you essentially need to address everyone who's every written about it before, and their arguments (or at least intermediaries who have already done that). A lot of philosophical texts are "I have this new theory", and the remainder of the text is "so-and-so said this, but they are wrong/my idea is different because...". Think of something like Kant's Metaphysics of Morals. The vast majority of the text is little different from a proof with QED at the end.

In physics, you learn formulas, and those can/do build on top of each other (as well as mathematical axioms/shortcuts). Reading Aristotle isn't any different in that sense. You aren't reading Aristotle for The Physics. You're reading it for ethical theory (and virtue ethics in theory), the underpinnings of philosphy of science, and Aristotelian/term logic (so you can understand the arguments of later authors prior to propositional logic).

In order to understand philosophical thought and argument, it's necessary to have this knowledge, and it's no different than me saying "in the process of studying physics, you have to study geometry" (as a prerequisite to later mathematics). This isn't any different, and putting the study of philosophy in some sort of "philosophy is slow" or "can only be understood in the historical and/or cultural context" box denigrates the entire discipline from a position of ignorance.