Your prusik is using two strands of the cord. For simplicity sake, that means it is providing twice the strength of one strand. So if you have a cord rated to 3,000 lb it would be 6,000, which would be on par with what you mainline would likely be.
That said, realistically you have strength losses in the prusik in knots, sewn eyes, bends, and splices, which reduce the break strength of the cord. So for this example you may actually be close to say 5,000 lb break strength instead of an ideal basket of 6,000 lb.
Lastly, just because 2 strands of the prusik could be rated to say 5,000 lbs that doesn’t mean the the cord may not slip on the mainline before breaking at 5,000 lbs.
You should check out some of “How not 2” on YouTube. They test knots, bends, prusik, the works. It will give you a better understand of the expect strength of some of these configurations.