Yes, for certain schools his having chosen less rigorous classes would decrease his chances of acceptance. But for some excellent public U’s that don’t seem to emphasize rigor as much, he might have a better shot.
What does he want to study? Where does he want to study? Private, public, in-state, out of state, in-demand competitive major versus wide open major, needs fin aid or not, there are just way too many variables here to be able to give any relevant advice.
He chose to take mostly or all regular classes, and overall did well in them, with a B+ average. In my state, which has a good flagship state U, I’ve seen kids who took no honors or APs, did no significant ECs, but did well in regular classes, get admitted right off the bat with their high unweighted GPAs, whereas kids who always took the highest rigor classes, played varsity sports, headed student government all 4 yrs, but got B/B+ grades in those highest-rigor classes, and hence had a lower unweighted GPA, got wait-listed (although eventually admitted off the wait list). Seems that in some states, the state flagships reward high unweighted GPA with little rigor over lower unweighted GPA with highest rigor. I think that selective private schools which have more resources to do a “holistic” evaluation are better able to factor in rigor, which would go against him. So if you’re in a state where the flagship state U looks at unweighted GPA and doesn’t much consider rigor, that might be his best bet, if it’s a fit otherwise.
Does he have standardized test scores? Does he intend to submit them? In his case, a good standardized test score might help him, but honestly, if you say that he is not a fast reader or writer (so much so that he chose not to do untimed extra written work), I suspect that he would not/did not do well on the SAT or ACT, and so should not submit it.
Keep in mind that the goal is to choose the best college for him, that the family can afford, that helps him to achieve his educational and career goals. That may not be the most selective school that he might be able to get into. For a young man who didn’t want to challenge himself to do the extra work, or take the most rigorous classes, and who is not a fast reader or writer, the best match might be a 4 yr state college (as opposed to the flagship U), or a 3rd tier private college with small classes, lots of academic support, lots of individual attention. He would very likely be able to get into any of those schools, and in fact, the 3rd tier privates might offer him a lot of merit money. Take a look at the several threads in the past few years for B students seeking recommendations - lots of great info in those.