Originally Posted by
Grinning Soul
Personal interpretation here, okay? This is *not* canon.
I think Jean's powers, especially her telekinesis, are only limited by herself. Personally, I dislike Teen Jean with a passion but, in my opinion, if she served for anything it was to show how much hidden potential Jean has. And this: that she has hidden potential, that she hasn't explored this potential yet, is now canon.
What that means, though, is open to speculation. So why wouldn't Jean have explored her powers more? Well, because her powers are, quite frankly, scary. Because she knows how much she enjoys being powerful and she has lived through a quite traumatic experience about what she can do when she loses control.
If you think about all the applications of what total mind-over-matter ability can do, you can understand why would be scared she'd lose her humanity. Just some examples: you can affect the biochemistry of any living creature, you can break atomic bounds and desintegrate objects/beings, you can change the vibrational level of atomic and subatomic structures, increasing and decreasing temperature, eventually affecting entropic levels, you can decrease movement so much you can reach 0 K (absolute zero), you can compress matter to the point of singularity and create a mini black hole wherever you want, you can fold space, change the orbits of planets, create wormholes, you can aggregate matter and compress it, you can ignite nuclear fusion and transform planets into impossible stars, you can move sub-atomic particles around to affect electricity, you can work with the whole spectrum on quantum probabilities and chose the most unlikely ones, etc.. etc... And that's only her telekinesis!
What makes her children seem more powerful, though? I think it's because they don't need to unlock their potential as much. I think Scott's DNA give them that potency, that impactful nature to their powers from the get go. Jean and Scott's children don't have the choice to hold back.
The question is, then: did they lose part of their potential in order to gain that "punch"? Maybe. They only have half of Jean's DNA. Who knows?
As for Rachel being the best host, yeah, you can argue that. But the problem is that people who argue that usually don't consider lots of factors around Rachel's experience with the Phoenix Force. They just bring the argument: "she did this and that and she was amazing and she never lost control".
They never seem to consider that she never held the whole Phoenix Force. At least one fragment was always with either Madelyne or Jean. And, at times, Force itself is shown acting towards Rachel like a mother, limiting itself, guiding Rachel.
That being said, Rachel was conceived and gestated by a Jean Grey who was merged with the Phoenix. Who knows how it affects her?
At the same time, while the Force keeps coming back to Jean, keeps saving her (in the shuttle, against Madelyne, near the sun), it seems perfectly fine abandoning Rachel.
So, you see? It's a complicated matter and people who make it seem simple aren't considering lots of other important things.