Yes, I believe that all had something to do with it. But it still leaves the issue of why those actors' limited availability and limited screentime was not better used. Rogue could have not taken the cure (as the alternate scene shows), Cyclops could have not died, and Magneto could have shown a bit more remorse over the curing of Mystique.
I never understood why people thought Rogue should not take the cure, like she was betraying her mutanthood or whatever. I think that was a special case, where her power was more of a disability than anything else, a power that would make her utterly miserable.
It's not like she was gonna be able to use that power in the field much, sure, she took Pyro's power and saved those cops, but it was not a power that, on it's own, would serve well in the field really, without putting her in incredible danger, that's why they gave her MsMarvel's powers in the books/cartoons.
I would have encouraged her to take the cure, she would have had a very unhappy life with the way she was, and it's not like she had any other powers, like the Rogue in the books/comics, where you could have said, well, you will be giving up the chance to save lives. Even then, I would have encouraged the Rogue of the MsMarvel powers to take the cure as well, she would have been miserable as well.
I think Magneto's attitude to a de-powered Mystique was in character from what we saw in the previous two movies, as was her payback betrayal.
Mystique wasn't only betraying Magneto, she was betraying that whole army of mutants.
Both instances showed how much their loyalty and 'friendship' was based on mutant-power, unlike the X-Men, who have regular friendships like normal people, that are not based on their mutant gifts.
Cyclops being killed off, eh, maybe they could have put him in a coma or something, but they were not planning on making any more movies in that series(due to the high salaries the actors would demand, as well as scheduling problems now they were all big stars for the most part), and killing him off served the story, and the problem of his character's absence from the film.
edit: But aye, they could have continued the series with another actor, or actors, I guess they thought they would just reboot, rather than continue on with X4 in that continuity.
I'm not one of the embittered haters of X-Men: The Last Stand - in fact I think the action scenes were exciting and the special effects very well done with no sign of being hurried - but I hope that those involved with it have learned their lessons. It would be great to read the inside story of what happened some day.
Unfortunately for Singer, his eagerness to do Superman didn't exactly work out too well either. An overly expensive production, a flawed plot and an excessive reverence to the Donner films are very apparent, despite the fact he clearly put his heart and soul into it.
No one came out very well from this whole experience. I hope now that the First Class franchise is a far more stable affair and that multiple films are mapped out at this stage. Even if those future films never come to pass, the pre-planned storylines could still be used in comic or cartoon versions just to finish the story. It's vital for this First Class franchise to have a structure, a consistency, and I hope the studio is listening to this. This one-film-at-a-time approach doesn't exactly create the best possible seamless saga.
Fox needs to be conscious of what has happened with the Avengers franchise (by which I am including the solo lead-up films) and the Dark Knight franchise, for examples of how to make a coherent series.
Aye, I agree of course, after or just before X2 came out, Singer even said words to that effect, that , like Peter Jackson with LOTR, and he gave another example I can't recall, he thought it was important for the director to oversee the entire trilogy, that they owed that to the fans.
I'm sure he regrets jumping ship now in retrospect, hence his involvement in FC, originally to direct. FC wouldn't exist in the form it is now if he had stuck to his original plan, as Singer had plans to use the Hellfire Club, with Sigourney Weaver as Emma Frost, so, there is a bit of a 'What If?' there, as in, would you have wanted him to do that, and sacrifice FC as we know it?
But I guess Singer and Vaughn would have come up with a good alternative plot if these characters had already been used in X3, Mr Sinister or someone like that maybe.