For the Black Hole feat, I reread the story Yes, it destroys solar systems over time, we literally see that being the case in the beginning of the comic. However, that is not what Captain Atom was referring to. That wasn't revealed to the JL until after the nature of the Black Hole/Mnenom was unveiled. At the time Captain Atom said that he meant "goodbye solar system" as though it was a normal black hole being able to do it. That means they put Superman to the task of doing that as though they believed he could handle a black hole that somehow can destroy a solar system through a timeframe and means they never specified. We know by basic science a dust-sized black hole couldn't destroy a solar system, because a dust-sized black hole would weigh about as much as a small planet (Here is the calc
https://vsbattles.fandom.com/wiki/U...Holds_a_Miniature_Black_Hole_.28March_2003.29), and on that basis alone we could potentially disqualify Captain Atom's word. Furthermore, we also know the reality that it wouldn't instantly destroy the solar system in the first place and that in reality, it would be destroying it planet by planet, but the JLA didn't yet know that and assumed Superman could stop a naturally occurring 4-B black hole. However, this can be seen as CIS/PIS because, in hindsight, we know the black hole isn't even solar system level anyways and yet its girth and gravitational pull were already straining and crushing Superman down even before it started unleashing psychic attacks. This means he was struggling with a 5-A to 4-C Black Hole, not a 4-B one, contradicting what characters implicitly believed Superman would be capable of.
Actually, in fact, how would Superman holding a black hole gives him 4-B? He isn't destroying it, just holding its mass and gravity to the best he can. Does Atom mean it would destroy the solar system if it somehow exploded? Well with mass-energy of 22.77 Foe, that would put a black hole at a mass of 2.53350418e28 kilograms which going back to my calculation prior to plugging in the mass would net 2e28 joules (High 6-A) to hold. Gravity waves are light speed, even by basic logic it should take a few hours to have its gravity reach the whole solar system, but let's ignore that and assume Captain Atom assumed the black hole had enough gravity to put enough pressure to destroy Neptune (Mass of Neptune * its gravity from 29.603330 AU away). Using this calculator, I get that giving the black hole a mass of 1646957 suns (2.60946805e36 joules or 5-A if you ask) which then inputting back and assuming Superman is 100 KG and the device holding the black hole is 1 cm in size, would make him endure 2.186366e29 newtons force, a lot of force, but not remotely solar system level. So by no means is holding this black hole going to even result in 4-B even if it can destroy the solar system.
As for the Solar System rocking feat, here is the calc
https://vsbattles.fandom.com/wiki/U....22Rock_the_Solar_System_.28November_2007.29; it is not 4-B.