It does make sense that Psylocke is capable of killing Magneto. Despite having the fight in a forest without too many metal, Psylocke is still uniquely equipped with the tools to take down the Master of Magnetism. She can use a psychic blade instead of relying on metal. She’s a ninja so she’s quick and she can get near Magneto. And if he ever makes the mistake of dropping his helmet in midfight, he’ll be vulnerable to her telepathic attacks.
Elixir would later pop in with Exodus to heal Magneto.
From – Uncanny X-Men Vol. 4 #19
I don’t follow Psylocke, but I have to assume that her powers were greatly wanked prior to this. Otherwise it makes no sense whatsoever that she could threaten Magneto. Way back, when better writers worked for Marvel, she put her psychic blade right into his head and it barely phased him, and she herself exclaimed how incredibly powerful he was. Now she’s a credible threat to him? He’s not generally vulnerable to psychic assault due to his considerable latent telepathic abilities (or the quasi-telepathic nature of his control of the electromagnetic spectrum). The helmet business is bogus but has been brought back by the movies. Anyway, whatever, the writer has Psylocke winning this round, however difficult it is to credit. I didn’t really buy her defeat of Mystique, either, at least the physical aspect of it, but again, that’s what the writer decided and presumably what Psylocke fans wanted to see.