Jubilee shouldn't be on this list. She hung out around Wolverine. Didn't get trained like let's say Kitty. I'd put Dani Moonstar above her. I believe Armor has some martial arts background. Heck, even Hope Summers. But the writer got some things mixed up. Storm, Warpath and Nightcrawler are not martial artist. Warpath and Nightcrawler are great fighters due to their power set and experience.
Kurt has swords training and James was trained to be a tracker and warrior - but no formal training in a discipline outside of their X-Men/Hellion duties. Storm is just brilliant and lacks a conscious. She'll wreck shop because she can and has to - thanks to her upbringing and sharp mind. Definitely one of the X-Men's best fighters - but not a "martial artist".
In terms of pure martial artistry - the top three X-Men should be Wolverine, Gambit, Psylocke (which ever). Those are three recognized masters of an art form. There's a difference when talking about "fighters" and "martial artists". The writer didn't properly make that distinction. In any case, Jubes has no place on either.
If this was "best fighters" Gambit might be edged out by X23 not because of her skills, but her power set and mind frame makes her a ball of unthinking death. But at the same time, Gambit was trained from childhood to beat the world's greatest assassin's everyday of his life. It's a good conversation. Gambit knows how to avoid being killed by being evasive. Something he's proven to be effective with against Marvel's best killers.
But again "best Martial artists" and "best fighters" two different lists.