As for resurrecting Jean Grey (for the 20th time, let alone the first time)... why mess with perfection?
Can't they just move on and create a new character?
The original planned storyline (with issue 137) was for Jean Grey to live and get a "psychic lobotomy" that would eliminate her powers, and then she and Scott Summers would marry and have a daughter named Rachel. All that was eliminated when Shooter as ed-in-chief mandated that she had to die because she killed 3 million asparagus-people.
I love how Claremont after a couple years was able to incorporate the continuity that he couldn't put into X-Men because Jean Grey had died. Claremont developed a parallel universe where Jean Grey and Scott had Rachel, and Rachel "time-slipped sideways" into the Marvel-continuity universe where Jean Grey was dead, and joined the New Mutants.
Which I think is actually more interesting and innovative than what Claremont and Byrne had originally planned!
And again, it's gospel at this point, one of the most read and loved storylines in comics history.
So why mess with that?
Why re-write popular continuity, when you could just as easily write a new story with originality, that wouldn't cheapen and bastardize some of Marvel's best-loved continuity?
