I think the thing is that other people using the Iron Man suit doesn't make them Iron Man, it makes them either a different hero/villain (War Machine, Rescue, Iron Monger, whatever) or it makes them a person temporarily using the suit.
It would be one thing for Jane to be worthy enough to pick up the hammer, but her suddenly having powers would be weird. Cap was worthy, so why didn't he get powers?
It's also wonky because the Jane Foster Thor is still supposed to be Thor and not a wholly different character. It becomes confusing if the movies start having to refer to Jane-Thor and Thor-Thor.
I'd be fine if she was the successor when Hemsworth wanted out, but doubling them up feels like it's unnecessarily confusing just for the sake of being able to go "OMG LADY THOR!" right now while everyone's still high on Captain Marvel and that big ladies-only scene in Endgame. Like it was a decision that was fast-tracked by the marketing department and not the writers' room.
I think Cap did get Thor's power when he held the hammer.
So on the wiki page describing her transformation, I don't mind it. They can play the cancer and love thing up. She only has the power when she wields the hammer plus it cures her cancer. Lots of possibilities.
Becoming Thor
A cancer-ridden Jane Foster transforming into Thor. Art by
Russell Dauterman.
During the 2014 "
Original Sin" storyline,
Nick Fury whispers an unrevealed secret to Thor that causes him to lose the ability to wield Mjolnir.
[27] Soon afterwards, an unidentified woman picks up the hammer, taking possession of Thor's power as the new Goddess of Thunder, and fights
Malekith the Accursed, Dario Agger (the new
Minotaur), and the
Absorbing Man. Although Thor initially attempts to reclaim the hammer,
[28] he – referring to himself as 'Odinson' – relinquishes the name and role of Thor after witnessing her wield its power.
[29] Odinson suspects Foster as a possible candidate for his successor,
[29] but he soon dismisses her due to her weakened condition from chemotherapy.
[30]
Angered that someone else is wielding Mjolnir, Odin and his brother
Cul, the God of Fear, send the
Destroyer after the new Thor to retrieve the hammer but Odinson and Freyja assemble an army of female superheroes to aid her.
[31] When the battle is over, Odinson asks Thor to reveal her face but is interrupted by
S.H.I.E.L.D. agent Roz Solomon, Odinson's last 'viable' suspect as the new Thor after all other possible candidates came to assist in the battle. Unbeknownst to Odinson, Mjolnir has given Jane the strength to fight as Thor while it is in her possession.
[32] However, Jane's use of Mjolnir has perpetuated her cancer as a result of the transformation process purging all toxins from her body, including the radiation being used for her treatment, each time she transforms.
[33]
Foster appeared in the
original graphic novel Avengers: Rage of Ultron as a member of the
Avengers.
[34]
The concept of Jane Foster gaining the powers of Thor had previously been explored in
What If #10 (August 1978).
[35][36]