Like you, I understood Destiny's systems prior to anyone really explaining them to me. I understood I had to do my dailies, do my bounties, get marks, and get my light up. So like any good Guardian, that's what I did. The entire reasoning to do this was simply to gear myself for "end game" content that was surely coming.
So then you're "raid ready" and you finally do the raid with like-minded Guardians, and you down Atheon, and you realize that raid gear *IS* better, and that raid weapons give you damage boosts to certain Vex within the raid, and it becomes apparent that the game wants you to gear up and do hard mode.
So now the next goal is getting to 30, because it not only heavily modifies your base damage, but it also implies you have some raid gear now, and then doing the raid on hard mode.
This isn't my personally take on how I should play Destiny, this seems to be how Destiny was intended to be played.