Being brilliant does not always translate into being a good student. The kids getting into top US schools are exceptional students + (the amazing ECs), unless they have a hook. And his cc grades won’t replace his HS grades for his GPA. But, he doesn’t need to go to a top school to do well. Students at any school can come out on top and shine, get Fulbrights, you name it. We have one at a good college (not top!) and get news all the time about the amazing things some of these students are doing.
Given that your S is not a fit with his HS, it sounds appropriate to either homeschool him or, if he has enough credits to graduate HS, he could do that and start at your state college. If he is brilliant and a good test taker, he may become a NMF and have more options for merit. Our S has a friend who had to grow up very fast due to a family situation, so he graduated a year early and got great merit aid at Oklahoma or Oklahoma State (can’t recall).
But, I would try to figure out why he gets Bs and Cs before sending him to college. It can’t be just the lack of participation that pulls his grades down to Bs/Cs. You want to fix the problem so that he can do well in the next stage of his life. I say this as a parent of a child who wasn’t performing to what we knew were his abilities before college, and the situation just got worse in college. (Also a bright kid -what I call average gifted - also a 34 ACT).