I disagree that it is harmless, as the lesbian character - with all that goes with that - is sidelined to accommodate Tamsin's crap.
And I also disagree that the others have anything like a function backstory. As far as we know Kenzi is both an abused teen runaway AND it wasn't so bad after all really, in fact she still sees her family.
Which is it? I don't know, do you?
And Lauren's "backstory" is a joke.
We know practically nothing about Dyson either - we saw Tamsin assigned to the police as "punishment". What about Dyson? What placed him there, given that it can only ever be a temporary placement since people will notice he doesn't age. Where else has he been for 1500 years?
And Bo herself - those ten missing years? What the hell was she up to? She was killing? Who? What informed that? How did she reconcile that. I don't know, do you?