Hmm.

From what I hear, she seems to have been very different from Reimu... but isn't that just because she was "filling her role" as a shrine maiden?

Her image as a shrine maiden was totally separate from her image as a person. Most people just weren't really aware of the latter.

Although, on the other side, there are some people whose role and personage end up becoming inseparable.

Not to brag, but I have some experience with that myself.

I don't really know everything about the system here, either... but I can see that Reimu is necessary for the running of Gensokyo, and fulfills that duty to perfection.

However, at the same time, she's extremely careless and untrained as a shrine maiden in charge of a shrine.

And yet, everything functions.

Well, that's easy to explain.

Reimu isn't "filling her role" as the Hakurei shrine maiden.