But Star Trek only makes sense when we assume one or two continuous timelines (e.g. normal Trek and mirror Trek). Otherwise there's no narrative.
Yet Next Gen's "Parallels" explicitly describes an infinite multiverse, branching for every possible outcome of any event, anywhere, ever.
Even Stargate, which treats time travel the same as Trek usually does, describes time travel creating alternate universes in "Before I Sleep"
IMO, saying the drama of an episode or movie is ruined because "in another tineline it went the other way", is equivelent to saying that the drama's ruined because, if anything bad happens at all, why dont they use time travel to undo it later?
The infinite other possibilities don't matter to the world the characters of our story are living in, therefore it might as well be one timeline. If that makes any sense.
And in the timelines we're viewing,the Borg are strangely inept villains,who have time-travel technology but can't seem to figure out what we can: that the further back Borg go, the more defenceless and vulnerable Earth is.