It's clear that the Milky Way has a structure like those, but it's hard to tell being in it.

We know less about the structure of our own galaxy than we do about many nearby galaxies like Andromeda. We literally can't see the forest for the trees because we are embedded inside our own galaxy, and interstellar dust blocks our view.

It could be replaced but only with another structure that is clear to all parties.

With so much irregular structure in the outer Galaxy, it looks as though the Milky Way is still growing, by cannibalizing smaller galaxies that fall into it.

... why I like timetables, because they make sure I don't get lost in time.

Off we go to the . . . Milky Way!