Nice to see this thread got refreshed!
My son was a high school Class of 2020 player whose final 4 choices were MIT, Caltech, Hopkins, and UChicago. He chose UChicago after getting a likely letter from admissions and applied ED. Everything went smoothly with the pre-read and likely letter just as the coach laid out, and there was little to no stress with the admissions process.
While both UChicago and Hopkins can offer likely letters to recruits who make the coach's top 6-10 list, you should be aware that neither MIT nor Caltech issue likely letters to athletic recruits so admissions is not a sure thing even with strong coach support. Of course, it's not a crap shoot either as the coach should be able to give you a rough probability of admission which could be around 50-70% assuming kid is very high on his list and has the top academic scores expected at MIT and Caltech. This odds range is obviously much higher than a non-recruited athlete's chances, but it's not 99.9% either like in the case of getting a likely letter.
Son loved his freshman year at UChicago, the school invited all kids to be on campus the whole year despite Covid and the team played a nearly complete season of baseball with over 30 games. Despite the cold winters, he loves the city and likes having a broad diversity of academic interests in the student body even though he is a STEM guy, and he really likes his teammates and coaches. He's also excited about having a free extra year of eligibility from the NCAA so he can play 5 years of college baseball, which turned out to be a silver lining in the dark cloud of Covid.
Good luck to your son with his options, he can't go wrong with either MIT or Caltech but they are very different schools, settings, and competitive baseball levels despite being premier technology institutes.