If I understand this correctly, he has never hit the 90's. That's just a hoped-for result in due time with ongoing training and avoidance of further nagging issues. His track record is that he tops out at 87 and sits below that, and let's say he has a plus curve ball.
First of all, that would generate a lot of interest in a typical situation. Especially with a 6'2", 170 lbs frame -- there's a lot of room to fill out there.
That sounds positive but maybe it isn't. Seems like all this was evident last summer and this past fall and yet, no offers. This leads me to think there is something that is being perceived about your son that is leaving people less enthused than the short description may indicate. It is often difficult for a parent to be objective in these situations, so it might be smart to ask your son's coaches for a "warts and all" assessment of how he is perceived. And actually, that communication should be handled by your son, because your involvement could become a negative in its own right, if indeed it hasn't already.
The JuCo option can be good, but how good depends on where you are. Here in VA, JuCo programs are few and far between in state, and those we do have would involve school at places where your son, based on his academic numbers, should not remotely consider as options for schools. In some other states, e.g. FL or CA, the JuCo options can often be more enticing.
I would actively pursue D3 options at this point. Choose based on which school your son would want if he never got to play baseball at all.
Then, if everything goes as you hope, some D1 offer may yet bubble up this spring, or even over the summer. With a D3, you sign no NLI, so the D1 options will still be available all through that period.