Bastilla was labelled a force and lightsaber prodigy by the Masters on the Dantooine Council during KotOR. I don't recall Vader (cyborg or pre cyborg) being stated or supported as being one. She was also noted as having exceptional innate talent with the force, so she ticks all of the boxes really: force strength, force prodigy and lightsaber prodigy. As a padawan, she was already considered a legend among the Jedi, a rising star among their ranks, and beyond most of the then current masters despite her lack of age/rank/experience. She was extremely prodigious. Her ability to form bonds (with Revan) also strongly speaks for her massive force strength, and this was even noted by the masters.
She was labelled a master swordsman, and the doublebladed lightsaber was her weapon of choice, a weapon that was pretty rare by PT times, and thus would be much more deadly to someone like Vader.
The experience she received on her journeys with Revan during KotOR 1 would had made her extremely powerful (Revan's party comes across literally hundreds of Dark Jedi during KotOR, so it can be assumed that Bastilla faced and defeated quite the number. That's just Dark Jedi, she would have also received loads of experience on all of the quests that go on through KotOR). She was already an extremely gifted and powerful Knight, so by halfway through KotOR (where she becomes a Knight) and by the end of KotOR 2 (where she's a Master), her improvement rate would have been huge (given the huge experience she received, her youth and her prodigy). The fact that she survived Sion and Nihilus' Shadow Wars also speaks volumes, and the speed in which she climbed the ranks is tremendous.
Not only did she receive training in the lightside of the force by the Jedi, but she was also given extensive training in the darkside by Malak. This can be seen when she knows of such techniques as force lightning and force drain. She was also powered up by The Star Forge to some degree (given that Malak was relying on her impressive Battle Meditation to defeat the Republic, he would have wanted to power her up as much as possible as long as there was enough power left for him), and as we know the power up would remain permanent, so her already extremely impressive strength in the force would have been further augmented by an imaginable tremendous increase.
Her lightsaber skills were clearly incredible, given that when she was a mere padawan, she displayed the ability to lightsaber tool a powerful Dark Jedi that had been accompanying Revan in mere seconds (it's in a cutscene at the start of KotOR). The Dark jedi was accompanying Darth Revan, so he was clearly one of the more powerful Dark Jedi, yet Bastilla, while still a padawan, completely owned him. That kind of tremendous an=ability while still a padawan makes you wonder how powerful she becomes by the end of KotOR two, with all her extra training and experience, and after being SF powered.
The fact that she was even given the responsibility to be part of the strike team that was responsible for capturing Revan speaks volumes. Now I know people will say she was only picked for her Battle Meditation, but that was to only ensure that the strike team would be able to board Revan's ship. She wouldn't have also subsequently boarded Revan's ship with the other jedi if they didn't believe she had the skills to be an asset. So the fact that the Jedi Order gave her so much responsibility (also seen when that let Bastilla in on Revan's true identity) despite her young age and lack of experience speaks volumes for how gifted a padawan she was.
Now when Malak blasted on Revan's ship just before the Jedi could face him, it knocked Revan unconscious and would have killed him if not for Bastilla. Not only did she survive and remain conscious after the ship had been hit (which had enough power to kill Revan), but she was also able to use the force to heal Revan and keep him alive.
Now all of the above is mostly not even mentioning her force ability, which is what she excels at. First off, her willpower was so incredible that she was able to force dominate a fricking Hutt. That alone puts her will beyond any movie character, given they all viewed such a feat as impossible, and thought of Hutts as being immune to mind tricks.
Another thing supporting her tremendous will (as well as force strength) is how incredible her battle meditation was. It was above that of people such as Nomi Sunrider (who could literally visualise something, and it would just happen: force her will onto reality), and so strong that she had the ability to turn the tide of wars instantaneously for a side that was seconds away from defeat and losing badly. her ability with the technique was so great that both the Jedi and the Sith (when she was one) literally solely relied on it for the war effort.
She's also displayed the force strength to instantly stun two very powerful jedi (Jolee Bindo and Juhani) pretty effortlessly. I don't recall Vader ever being able to force own powerful force users like that. Now what people don't seem to get is overpowering any force user, no matter how you do it, always requires the same power, and that is the power to break through their force defence. In other words, if she chose to, she could have just as easily been able to instantly kill both of them on the spot. Now seeing as how people go on about Exar Kun force owning Odan-Urr like he did, and Traya owning those Jedi Masters like she did, you have to view what Bastilla did as even more incredible, given she did it instantly.
Her stats are also pretty damn uber (in comparison to the others), and they only grow way more powerful after she turns to the darkside. In sticking to the nature of her class when levelling up, she can become pretty uber. In particular, I’d like to note that Vader’s main strength is the fear he inspires in his opponents, yet Bastilla has a force immunity to fear.
Face it, Bastilla pwns.