Already addressed: this reflects TMP's decades-old retcon of the Klingon appearance
Which DS9 un-retconned in "Trials and Tribilations."
First, let's throw out "predictable"; continuity has absolutely nothing to do with whether or not you can predict what happens next.
It does with time travel. Traveling into your own past means you already know what's going to happen next, because those events are in the past for you. If those events DO NOT play out the way you expect them to, it's either because your knowledge of the past is wrong, or you're in an alternate timeline that is no longer continuous with your own.
The reason it's not CONTINUOUS is because your actions will not contribute to your younger self traveling through time (Temporal Investigations' "Predestination Paradox" or a causality loop), assuming your younger self travels through time at all. In this case, it would only be continuous if through a series of retcons we find out that Spock Prime is the same person as NuSpock after all and that everything he's told his younger friends/self are actually highly veiled references to his own past.
We're left with "one event logically follows from another" - such as the creation of the alternate timeline as a result of events in the Prime timeline.
But the Abramsverse wasn't altered by events in the prime timeline. It was altered by events in its OWN timeline.
how can one arrive in a timeline whose very existence is dependent on one's actions subsequent to arrival?
You can't. The timeline would have to be pre-existing for you to travel to it in the first place.
You could say (without any actual evidence) the two universes were
identical before Nero arrived and that the differences occurred at that point. It's still, however, a parallel universe to which he traveled, and it doesn't necessarily follow that they WERE identical in every respect.
Events originating in the Prime timeline created the alternate timeline
No. Again, the timelines supposedly diverged in 2233, not 2387. The latter would have been the case in, say, First Contact, where Enterprise is caught in the temporal wake of the time vortex and is "somehow" protected from the changes in the timestream; in effect, they FIRST enter an alternate timelime in which the Borg of conquered Earth, and THEN travel into the past of that timeline to alter that timeline.
They share a history prior to 2233, barring other time-travel shenanigans about which we don't have specifics. But the relevant "history" here is that the Abramsverse is a branching timeline which branched from the Prime.
Obviously. But we are not totally sure WHEN. NuSpock thinks it happened as a result of Nero's arrival, which is a fine theory, but he is not (and really, cannot) take into account all the OTHER time travel events that would have been effected by that event, mainly because he has no way of knowing about them or their significance.
In particular, the Enterprise in this timeline will never discover the breakaway timewarp equation; they will never travel back to the 60s and meet Gary Seven, which will have certain implications for human history through the 20th and 21st century. From Spock's point of view, those implications are already manifest, but he is in no position to realize that Nero is ultimately the cause, or that anything different might have happened at all.
That makes no sense at all. Would he really be that illogical? Why would the Prime timeline cease to exist because Nero destroyed a planet in the Abramsverse timeline?
It ceases to exist for Spock, because he is not IN the prime timeline. History cannot and will not unfold the way he remembers it, and even the events that originally caused him and Nero to travel into the past will never actually happen. The timeline, in other words, is
history as the universe knows it. That history has now been erased.
He could, of course, have the Guardian of Forever zap him into a different timeline, or he could do a favor for Q, or his house could get sucked up in a tornado, or he could sip on a banana peel and fall into Quinn Mallory's wormhole experiment, any one of which might catapult him into an alternate reality. In doing so, Spock would literally change reality and history would unfold differently; Vulcan may exist again, or Vulcan may have been eaten by the planet killer, or Vulcan may have been putted into a black hole by Trelane in a fit of boredom. UNTIL he changes reality, only the timeline he is currently in is real.
Weren't you the one who was saying events in one timeline couldn't have an effect on the other?
Yes. I also said BECAUSE of this, only one timeline can be considered "real" from an individual's point of view.
No they didn't. Neither did the Bajoran conquest of Cardassia or the Borg assimilation of Earth. These things happened in OTHER realities that are not related to the Abramsverse. The Hobus event is only related inasmuch as its effects Nero mind, but the timeline is affected by Nero's ACTIONS, not his memories.
You mean they can't "re-happen" in the alternate timeline
No, I mean they can't
happen. Any given event can only occur once in the linear timeline.
The existence of the Prime timeline is not somehow dependent on the Abramsverse timeline changing into the Prime timeline.
Indeed. That's because it is a PARALLEL timeline, and the two of them no longer have anything to do with each other. The primeline doesn't exist for NuSpock and NuKirk and arguably never did. Significantly, it doesn't exist for Spock Prime either, even if in his personal past it did until recently.
Their shared continuity can easily be seen given that the same character departs from one and turns up in the other.
Incorrect. Nero's
memories are affected by what he experienced in the alternate timeline, but his memories are no longer consistent with reality. Under normal circumstances, that would make him delusional; in his case, it's not really his fault, because
reality itself has actually been changed.
Case in point: Nero insists that Romulus HAS been destroyed. He saw it happen, he remembers it happening. But if he went to Romulus right now, he would see the reality that Romulus HAS NOT been destroyed, that it really is there, and that none of the things he remembers happening are real anymore. It would be the exact same situation if Spock ALONE had traveled back in time and destroyed Hobus and Nero, through a First Contact-style vortex, wound up in the altered reality with his original memories. From his point of view, the destruction of Romulus has ceased to be reality, because reality has now been altered; the only reason he continues to
treat it as reality is because he is insane.
I use "overall continuity" and "multiverse" interchangeably
That's probably not such a good idea.