First of all, I want to start out by saying that Jean Grey, while powerful, is nothing compared to Storm.
Regarding Jean's telepathy vs. Storm's mental defenses, when Storm started out as an X-Man, her mental defenses were not strong at all and literally every psi she came across was able to take her down (Mesmero, Emma Frost). However, as her character progressed, Claremont would spend the better part of 17 years building Ororo's mental defenses. As her mental defenses grew, she was able to best the likes of Emma Frost (a more powerful and more skilled telepath than non-PF Jean Grey), Shadow King (who dwarfs Jean in both power and skill), Dracula, and others. As a matter of fact, her willpower was on a constant growth curve that it got to the point where no single telepath could prevail against her mental defenses. In Uncanny X-Men #277, for instance, the Warskrull had the combined power of Xavier, Psylocke, and Oracle, and tried to kill Storm with a mindblast. The best he could do was temporarily subdue her, but freely conceded that given time, she could well break through his mind attack. So, before she could beat out his telepathy, he tried to have Lilandra behead Ororo with a sword. Xavier by himself is much more powerful than Jean Grey, and added to that power in this instance was, again, Psylocke and Oracle. As a matter of fact, Storm's mental defenses were so unbeatable that Nanny regressed Storm to a girl of about 12 years of age, giving Storm amnesia in the process. She did this to weaken Storm's mental defenses since Ororo's strength of spirit was too indomitable to be beaten. Even while in this regressed state with her willpower diminished, Storm was able to beat back Shadow King's psychic attacks.
During the 90s, Lobdell, Kelly, Seagle weakened Ororo to prop up Jean Grey and stripped Storm of her mental defenses. Literally, every single psi she came across could take her down save for one instance where she was assaulted by a lowly Morlock telepath. However, when Alan Davis came along, he reinstated Storm's indomitable will which was again stripped from her by Claremont during Revolution to prop up Jean who was on the team with her. However, once Jean was off the team, not only did Claremont reestablish Storm's mental defenses, he added the extra boost of her being able to use the electrical forces inside of her body to literally fry invading telepaths out of her mind. She used this to beat out Bogan, a Xavier-level telapth. And added to Bogan's power was the the psi or Rachel when Storm EASILY bested his mind attack.
Nanny explaining how Storm's willpower as an adult was too strong, so she regressed Storm to childhood to weaken her willpower:
http://2.bp.blogspot.com/CLag1t1LwWq...0PpU6NMs=s1600
Regressed Storm beating Shadow King's mind attack:
http://2.bp.blogspot.com/ttG9ECvDL8t...jz2OXP8a=s1600
Storm vs. Bogan-Rachel:
http://2.bp.blogspot.com/ncdiOxD3Vz1...LlMMyWXc=s1600
http://2.bp.blogspot.com/B7jnrg0yHNx...a_VmhgSw=s1600
Now, Storm vs. Jean's telekinesis:
Here, we see Storm attacking Legion with winds so strong that Jean's TK, who is only getting a taste of what Storm is dishing out against Legion, can only withstand it for a short while:
http://2.bp.blogspot.com/suBGJypc0Y5...RYT_aq1-=s1600
Here, we see Storm wield her lightning with power that the impact of shards of glass being hurled by Storm's lightning strain's Jean TK:
http://2.bp.blogspot.com/OzuRbP-k818...GliOTO81=s1600
Then, on top of it, Storm doesn't even have to try and knock down Jean's TK shield to get around it. She has plenty of ways of shattering Jean's concentration like pulling stuff like this:
Using thunder and lightning to render it impossible for the Brotherhood to concentrate:
http://2.bp.blogspot.com/BVeoOq3pMbD...L-qhEZz-=s1600
And then there are the two scans where Storm shatters Jean's concentration with creative applications of her elemental powers so that Jean cannot access her psionic abilities.