@mutterphone I hope you don't mind me saying this. I don't have a child at O or C, but I do work in a university.
I know you've explained that your DT1 doesn't like to make a fuss, but it seems to be clear that the experience he's having is very different from that of every other student whose partner has commented. It's also very different from that of your DT2, of course, but that's a different university.
I can't help thinking that if things continue like this for your DS1 all through the year then by the time the exams come round in the summer he'll have had virtually no teaching or direction. He shouldn't have to speak up, but I think the sad reality is that he's going to have to if he wants anything to change. I think I remember you saying that the tutor who hasn't marked his essays is also his Director of Studies. That's unfortunate, but I think that makes it all the more important for him to speak to the tutor, because he can't call upon his DoS to help in the way that most of the other students will be able to.
Also, the pastoral tutor hasn't been in touch all term? That's completely inappropriate too. These are difficult, busy times, but where I work we've been turning ourselves virtually inside out on a daily basis and doing lots of unpaid overtime since March to try to make sure that this term goes as well as possible for the students. One would hope that staff at all good universities would be adopting the same approach. Clearly your son's tutor isn't.
So, I think he needs to speak up. He's entitled to have his essays marked, and he should have them back before the holidays (or at the start of the holidays, now that the holidays are almost here) so that he can review them. He also should have instruction on what he needs to read before next term, and does he have exams in January? If so then presumably he needs some advice about that?
I'm so sorry to hear about the experience he's been having - it actually makes me quite angry, because I know it doesn't have to be that way. If the tutor is too busy then he needs to discuss that with the college, and they need to arrange for his duties to be split. Your son has worked hard all the way through school for this experience, including having taken a year out to re-apply, and it's simply unacceptable for him to be treated so casually.
I hope you and he can get this sorted out.