John would find new and more complicated ways to screw over people. Not necessarily out of malice, but because he's likely to overestimate his capabilities once smaller issues become easier to deal with.
As someone pointed out, it's likely that if he applied the Wisdom of Solomon to "doing my homework" it would likely tell him 'if you do this you're going to regret it' because the logical inference would be that 'this is easy to solve as Captain Marvel but the material is for the betterment of Billy Batson, and you won't get better unless you solve it as Billy'.
But if you struggle in school, logically, you can also absolutely use Solomon's Wisdom to do better. Transform, create a study plan, figure out a dozen ways to explain complicated concepts in a way a child will be able to understand, write out the problem and then a step-by-step breakdown, and so on.
That's not me saying "LOL comic book characters aren't intelligent enough to use their powers correctly", the logical explanation for why they choose not to do so is that these powers go to people who have a strong enough moral foundation to believe this is "cheating", that using superpowers to get ahead of normal people is 'bad', which isn't entirely to their detriment since many alternate universe scenarios conclude 'if the right sequence of events takes place, anyone good can turn very bad, and the consequences for that happening when the good person has superpowers is also magnified'.
But Batman isn't even worse for the external advantages he possesses, which undermines this narrative. It's not annoying that Billy won't try to help himself out with his abilities, it's annoying that the same setting is narratively inconsistent about it.
