I agree when it comes to manipulating electro-magnetic energy, Polaris should be ahead of Storm as its her main power. Now when it comes to feats, Storm has Polaris beat. Storm has caused a global disruption of the Earth's Em field, opening up a hole in the Earth's Em field, created a protected force field around the planet to block a solar flare, flown on solar wind and created lightning in space to stun starships.
Now with that being said, I'm not saying Lorna couldn't replicate these feats but sadly, she has never been in a situation where she could display her powers that way.