Storm is barely in X2, so I don't know what you were watching. The scene with Nightcrawler actually had to be rewritten to include her because Storm had so little to do in the rest of the movie. A "female lead" has nothing to do with action scenes, it has to do with participation in the story and relation to other characters.
Jean was the female lead in X2:
1. The female lead is traditionally the love interest of the male lead (Wolverine : the protagonist)
2. Jean has her own arc in the film: she's established as losing control of her powers since Liberty Island and that storyline is resolved by the end of the film (Jean's sacrifice). No other female character has an arc in the film or a significant storyline.
3. Jean's storyline is a (subtle) mirror of Wolverine's storyline: Wolverine is going on a external journey/quest of self-discovery. Jean has an internal journey of self-discovery of her powers (clearly less time is spent on her journey).
4. Jean's storyline has a climax (Jean gains control of her powers and saves the team) just as Wolverine's does (his final confrontation with Stryker). Jean's is arguably the bigger one even.
5. Jean is part of the love triangle subplot that actually gets multiple scenes in the film and is a continuing subplot from X1. Storm doesn't even have a subplot in the film.
6. Most of the denouement of the film (i.e. the part after the climax) is spent on characters (Wolverine, Cyclops, Prof X) reacting to Jean's sacrifice. Jean even closes the film with narration hinting at her return.
Well, all that wasn't addressed to me, but I want to say this:
You've proved Storm wasn't of any significance in X2. And more or less proved the point we are all making: that justice hasn't been done to the character.
Even Jean's arc in X2 wasn't perfectly done, to be honest. We're told she hasn't been the same since Liberty Island (and no mainstream viewer would connect the dots between that and Magneto's radiation machine doing something. In fact no one really knows what happened to Jean at the Statue of Liberty. Did that machine evolve her? Break through mental blocks? Did Singer even envisage the mental blocks concept in his vision of what was happening to Jean?). Jean later has a far-too-brief fight with Cyclops and then is found twitching on the floor behind a generator, somehow having hurt her ankle while Cyclops is walking perfectly well from being flung through the air and across the entire generator room.
That's not to say X2 was bad or weak but it sure ain't perfect.
I didn't mind the role Storm had in X2. The conversation with Nightcrawler works pretty well as another 'mirror' - his outer 'ugliness' and inner beauty against her outer beauty and inner ugliness (anger, fear). Halle seemed a bit watery-eyed in that scene, though; every time I watch it, i feel she is about to burst into tears. However, it was a nice moment, even if the 'I have faith' scene at the dam later was a bit undeveloped and cursory.
It's clear though that Storm is a popular comic book character - and there must be a reason for it, so the filmmakers need to ask themselves why she is popular, what it is people like, what makes her tick.
She's had her own journeys of discovery too. She lost her powers (later exploring her heritage and purpose in Lifedeath), she has had romances (with Forge and Black Panther, and even with Dracula), she had a Phoenix-style out-of-control power progression (in a storyline with Doctor Doom), she sacrificed her physical body as the X-Men faced the Brood race, she discovered a mystical/magical heritage. In the Wolverine and the X-Men animated series, she was manipulated by Shadow King and her powers went out of control, causing destruction across Africa. Bottom line is there is plenty of scope for character development, subplots and arcs. (Plus it would also be chance to do some amazing and visually-stunning location shooting in Kenya or Egypt!).
The fans aren't asking for Storm to dominate, just to have a bit more dimension and a sense of purpose as to why she is there.
