Issues with Time Travel in Slaughterhouse 5

 skip this post and read "so it goes" if you want something more book-related and understandable. 
There seem to be paradoxes in Vonnegut's portrayal of time. I don't mean this as an indictment of the book per se... it's still good fiction, and it makes as much sense as it needs to. I just wanted to try to flesh-out exactly what's been bothering me about the timeline. It's difficult to talk about. I apologize if I stop making sense.
My first issue is that the book assumes a super-time, like most time-travel stories. This is my term for a timeline which the time-traveling characters and usually the reader follow. I don't know if there's an actual name for this-- other people have probably also noticed that it's a thing.
When there are different versions of the same 2016 (for example, one like ours and one that's been decimated because the main characters accidentally went back in time and, like, detonated some nuclear weapon or something), it's obvious that there's a super-time. There's an earlier, unchanged 2016, and a later, messed up one--nominally in the same time, but in different super-times. There's a younger Dr. Who and an older one, even though each exists in any time period. Dr. Who is aging in his own super-time. The Tralfamadorians exist in every time at once, yet they change--chose to visit different times in different orders, choose to spend more of their super-time at the zoo than in wars.

 Vonnegut doesn't fall into the trap of letting things that have already happened change(not outwardly anyway--I'll come back to this)-- I have to give him credit for that. To Vonnegut, either 2016 is blown up or it's not--there aren't different 2016s in different states. This book's got a very deterministic outlook which wouldn't fit well with people reordering the past from the future. (Without freewill, what would make each iteration of characters different from the next--what would make it so that a previous version of each character hadn't gone back and blown up the world in the first place? I recognize that doesn't make sense. It's the best I've got.) Due to this consistency, the book's super-time is less obvious. It still exists, I think, and though I don't know that super-time is problematic, it sorta seems paradoxical to me to separate time as a medium you can travel through from your super-time that you exist in/progress in no matter what. Or, at least, it seems like you're not properly traveling in time unless you also travel through super-time.  And Billy does seem to be stuck in his super-time. He's progressing: learning about his past and his future. He gets dislodged in time at a particular point in his life, which implies that each time he returns to a point, he's a little different. He has different memories so he knows more or less about his future. So there are different Billys that people are interacting with at any point in time. Which Billy is Weary beating up in the German woods? all of them? a different one for each iteration of Weary?(super time sort of assumes infinite iterations of the same time period--one for every moment of super-time). This seems problematic to me.
Also, it's strange that, given that Billy is different every time he goes somewhere, he wouldn't do different things each time he visits an event. Even if you don't believe in freewill, it would be difficult to argue that different people with different experiences don't act in different ways--a Billy that's seen his death 20 times might act differently than a newly unstuck Billy. Is Billy just that passive, that no matter what he's been through he reacts in the same way every time he is in a certain situation? Even if "one of the main effects of war, after all, is that people are discouraged from being characters", that seems a little far fetched.