Farther proofs that Jacen's power rivaled Luke.
Fallanassi Akanah:
"You have the same power I once sensed in your uncle Luke, but without the light."
Jacen inside the ship in which Thul crushed:
"Jacen used the Force to slide several tons of cargo deck into a secure position, then walked..."
Luke uses TK on a B-Wing:
"He grabbed the vessel in the Force and held it in place, then opened fire with his laser cannons. The startled B-wing pilot applied more power, trying to break free. Luke drew on the Force more heavily to counter the maneuvering thrusters, and all of the energy flowing through his body began to make his skin nettle."
Jacen replicates Luke's feat:
"Luke started to Force-grab the fighter again, but Jacen had already caught it and was holding it in place while cannon bolts pounded its shields from above."
Jaina:
"I've known him to move star-ships, deflect ion cannon... even turbolasers. He can hear at huge distances with some Theran Force-listening tech-nique. He can create elaborate Force illusions that feel real, he can walk into the past or future, he can control objects like scanners, and he can mind-rub-he even mind-rubbed Ben.""
Jacen uses TK on a huge Chiss assault cruiser:
"And that was when a loud groan sounded from the hull. Jaina and Zekk paused, thinking the craft was about to explode. Instead, it rolled away from them, revealing a dark jagged hole where the near wing had once connected to the fuselage.
Realizing someone had to be using the Force, Jaina and Zekk glanced over their shoulders and found Jacen looking in the drop ship's direction. He smiled, then nodded past them toward the vessel."
Size of that cruiser:
"The vessel itself was a fiery wedge of ceram-metal composite at the tip of the smoke plume, no more than forty meters long and perhaps half that at the base."
Jacen deflecting cannon bolts of that cruiser:
"Jacen holding his hand above their heads, cannon fire ricocheting away as though he held a deflector shield in his palm. That was something Jaina and Zekk had never seen before."
Strength of those bolts:
"Unlike blaster bolts-which carried very little kinetic charge-the charric beams struck with an enormous impact. Several times Jaina, Zekk, and even Lowbacca felt their lightsabers fly from their grasps and had to use the Force to recall the weapons.".
All feats above were performed before Jacen became even more powerful by turning to darkside. He, also, displayed those feats without drawing on pain, rage or any other strong emotions.
Good example that injuries don't affect Force powers of those, who can ignore pain:
"A disk buried deep in his forehead, one of the Sun Guards twirled in front of Plagueis like a crazed marionette. Blood fountained turning to mist.
...
Plagueis pressed his right hand to the right side of his neck to discover that a disk had made off with a considerable hunk of his jawbone and neck, and in its cruel passing had severed his trachea and several blood vessels. He cupped the Force against the injury to keep himself from lapsing into unconsciousness, but he fell to the floor regardless, with blood pumping onto the already slick stone circle. Around him, slanted in his faltering vision...
...
Having run himself through a similar test, Plagueis knew that he had lost a great deal of blood, and that one of his subsidiary hearts was in fibrillation. Sith techniques had helped him perform chemical cardioversions on his other two hearts, but one of them was working so hard to compensate that it, too, was in danger of becoming arrhythmic.
...
His second subsidiary heart failed, paralyzing him with pain and nearly plunging him into unconsciousness. The assassins wasted not a moment, throwing themselves at him in groups, though in a vain attempt to penetrate the Force shield he raised. Again he rallied, this time with a ragged sound dredged from deep inside that erupted from him like a sonic weapon, shattering the eardrums of those within ten meters and compelling the rest to bring their hands to their ears.
In blinding motion his hands and feet smashed skulls and windpipes. He stopped once to conjure a Force wave that all but atomized the bodies of six Maladians. He spun through a turn, dragging the wave halfway around the room to kill half a dozen more.
..." - His injuries were far more lethal, than Jacen's and, yet, he displayed the best feats from entire book.
Sidious assessing Plagueis:
"Sidious had been wondering if Plagueis had been weakened by the attack, but he saw now that, for all the punishment his body had sustained at the hands of the Maladian assassins, the Muun was no less strong in the Force.
"Your thoughts betray you," Plagueis said. "Do you think that Malak's powers were weakened by Revan's lightsaber? Bane by being encrusted in orbalisks? Do you think Gravid's young apprentice was hindered by the prosthesis she was forced to wear after fighting him? "
Unlike Plagueis, Jacen did not only ignore pain but was getting empowered by it. Assumption that during fight with Mara Jacen's Force powers were weakened by far less lethal injuries than Plaguies' is as biased as it could be.
My point stands. If Mara could resist Jacen - descendant of Chosen One who's power rivaled Luke, I don't see why it would be so impossible to resist Vitiate.