If you are a D1 school, and you have a bunch of 2020 HS kids now finishing Juco, and others in the transfer portal, wouldn't you rather take a kid who can help you win now rather than the 19 year old 2022 HS senior? Kid can crush it all he wants against other 22s. But the Juco kid is more proven and helpful...I think?
Francis, you are really starting to recycle the same questions over and over with slightly different window dressing.
If the D2 is offering your son now, then now is their timeframe. Based on all the info you and your son have gathered, is it a good offer or not? Is it a good fit or not? You've already established that another D1 offer is not likely to come up between now and May at the earliest. So what is the difference whether the current D2 offer is 2 months or 5 months or 8 months earlier than what the "norm" is?
Regarding D1 schools looking to JC transfers before a HS senior, you know that many schools use JC kids and many don't. That isn't likely to change significantly. Until that time that your son has the additional D1 offer/s from specific school, there is zero reason to speculate. You already know that, generally, the pipeline will be more crowded. That is as much as you can project.
Unless you and he pick a program where he will surely play (which, to some extent, says you guys are under-shooting), there will be some risk, some heavy competition and uncertainty. That's where the player... every player.. has to step up and earn his keep. Then, he will have to do it again the next day, the next week, the next game, the next year. That's competitive college baseball.
At the risk of diluting my primary message above, here's another thought...
If the D2 offer seems like the best and smartest choice at this time, he should take it with the idea that he is fully committed to it. If things change drastically (i.e. - he improves significantly over the next 8 months and gets more serious D1 attention), things can be re-evaluated at that time. Most coaches, under those circumstances, would be inclined to understand. Probably even more so in these unprecedented times.