It's important to read the proposal, and yes it's not simple to understand. Page 44 illustrates payload comparisons. Note. They do NOT claim that the J-232 carries more payload than the ARES 5. Au contraire. What they do say is that the standard A1 + A5 mission profile carries less payload than using the two Js. In other words they change (improve to my taste) the mission configurations using the Jupiter more off-the-shelf hardware yielding a mission profile superior to the ARES new development with its lower TOTAL payload to LEO route. Reading the details, their entire approach meets NASA's stated goals much better than ARES.*

Another BIF plus is that the J-120 allows ISS resupply because it carries a cargo payload as well as the Orion crew. It's notable how much weight is pissed away (see other topic) by flying the Shuttle airframe to and from orbit. Yah, Raoul has long been a capsule advocate and does have some valid rationals no matter how much "Back To The Future" Apollo Done Over irks me.

* So, these internal rebel team guys are either simply WRONG or a management beuracracy is afraid to admit they're not on the right path.