I think you already have some good answers. At Michigan and at other very selective schools, there is somewhat of a lottery component. That is, there are a very large number of people with stats that get them in the “bucket”, but then after that decisions have to be made to cut that group down. Even for in state kids, odd things can happen. I know two kids from last year who were in state, got into Georgia Tech, but were deferred from Michigan - one got in on the last round, the other never did. Oddly, one of them had a cousin in Georgia who got into Michigan, but not Tech (their parents joked that the kids’ dreams of going to school together did not work out).
The essays are a chance to impact your “lottery” some. If your son is a junior, he has plenty of time to work on that. Michigan has four essays of its own. I am told they are using those as a chance of really getting a sense of the kid and fit. Think carefully about how you want to come across in those. The more you know about the school, the more you can show the parts of you that would shine there.
In addition, more than one visit would help also (not just getting in, but his decision of whether he likes the place). You can do a University visit, but also COE has their own as does Ross etc. If he might be interested in more than one, hit them all. It probably is not too bad of a drive. If he can do it this summer, see if they have any summer camps that match his interests. Some of them say they have no impact on admissions, others don’t say one way or another. But it is a credible commitment on his part that he understands the place. There are a ton of camps run in engineering and the sciences. All of these will give him things he can talk about in the essay and, more importantly, a real sense of the school.
Also, call admissions (maybe wait a month or two to let them get past the current rush). Go over your kids schedule and find out if there is anything they are looking for. I know people who did this at Michigan and at some other schools. They get different answers, but you still have senior year to adjust some. For example, I know a kid who wanted to do engineering. He had enough “english” credits with AP junior year and some elective classes Sophomore year that his plan was to just take one term of Speech, which counted as English, his senior year. He got the idea from a tour at one of the tech schools where one of the speakers said load up on math and science by cutting English, History etc to the minimum. But his family contacted a few schools, including Michigan, that said they would not be positive about a year without English (and that was the COE). They did learn that every tech school they spoke to said AP language was nice (more rigor is always better) but the 4 years he had of language was enough. When their daughter was applying a year or two earlier, she was told the AP language was huge in looking for engaged kids. She went to Brown ED. So her parents just took the suggestions from her and carried them forward. But she had been thinking probably history or political science (she wants to go to law school).
Finally, what is the success rate at your high school for Michigan in general? It is my understanding that they (and I know several other colleges) heavily weight what they know about the high school when looking at grades etc. I don’t know what to make of a high school that has 4 kids graduating with perfect grades and a 36 on the ACT. Given that less than 3,000 kids earn a 36 each year, it suggests this must be a very advanced high school. I would think your counselor might need to work with Michigan to make this point. That said, if a ton of kids are graduating with perfect grades, it may make it hard for them to assess the transcripts. Similarly, at my kids school I don’t think you could get 14 AP classes. It just would not work in the schedule, plus they really push the kids to not take more than 3 a year (and 0 Freshmen year, with the only option being the CS AP class if kids pick it). While a few AP’s are only one term, a lot of them take up an entire year. So with only three years, a kid would really have to max out to get to 10. I don’t know any kids who did (and we do have lots of kids getting into “elite” schools, last year included Princeton, Stanford, MIT and Harvard off the top of my head, though those are far from the norm) If there are a bunch of kids taking 10+ at your school, then maybe they give less credit for it (particularly if they are not scoring well on the exams). Imagine you are the AO reading files. If everyone from a school has a bunch of AP’s, it may not look as special. So your school counselor would need to help them understand why these kids should not be compared to each other. Harder to see why they would ignore 36’s given there are so few. But I have seen statements from AO at top schools saying things along the lines that they really don’t see a 35 as being different from a 36 - once you get to the top categories the variation is less predictive of performance. Still, I think something like only 15,000 get a 35 or above and they probably are not all applying to Michigan.
Sorry this is so long. Hopefully it will give you some ideas on helping your son. If Michigan is the right place for him, it would be worth it. But working through all of this may help him decide it is not the right place.