It's really hard when you feel like your DC's DF can't be bothered with them isn't it? And I feel for you. And DS.
But the reality MIGHT not be exactly as you are seeing it from your point of view. Your ex's POV mught be different...
One night every week is pretty much the equivelent of what many, many NRP do isn't it? (two nights a fortnight - every other weekend). So he isn't totally different from the norm. Would that work better for him? Friday night to Sunday evening...that way you'd both get a full weekend with DS alternate weekends.
TBH I think his point about school on Monday morning could be valid. Many NRP do drop at school on Mondays, but that can cause extra complications for both the NRP and the child. As the RP, one will normally have sorted working hours that facilitate the school run, or made other arrangements. But the NRP might not be able to start work late every Monday or every other Monday, or to make other arrangements for just one day a week/ a fortnight. And it often causes difficulties for the child because they find they don't have their PE kit/homework/particular book 'because it is at DM's house.'
If he only has him for one day a week, I don't suppose it's the biggest issue in the world if he hasn't made him wash/bathed him (not sure how old DS is), though I do know how irritating that can be. And ex might feel that he and DS only have one day a week together so he doesn't want to have to do the routine stuff too much. That might be annoying, and I'm sure some MNers would think I am wrong to condone it. But I (particularly when DCs were smaller) always made sure they'd done their homework, for example, before they went to ex's so they didn't have to spend their more limited time with him doing stuff like that. So I don't mind if they come back unwashed, as long as they come back in time to wash here before bed.
And, while this is obviously making you upset, do you REALLY want to NOT have your DS for the whole of every weekend??
Regarding taking DS to family members. I think you need to be clear about whether he is actually 'palming DS off' or is actually, as he claims, facilitating DS's relationships with his wider family (it might be either - I don't know and am not making a judgement). My DCs see their paternal family when they are with ex. Sometimes I feel like you do about it, but on the other hand, DCs enjoy that time, and I'm certainly not taking them to see ex's family when they are with me, so if they are going to have a relationship with them it has to be in 'his time.'
I guess WRT maintenance, if it isn't about the money, I wouldn't bring it into it. If it is about the money, why don't you start off by popping the figures back into the CSA calculator and seeing what it spits out? Because the days with the NRP are in quite wide bands, when you take into account the time ex hs DS in the holidays etc (if he does), it might not change the calculation a great deal or at all.
Finally, please don't feel that I am belittling your feelings, or siding with your ex, because I'm not. I think I'm trying to say that we each (all of us) have our own reality (in this case RP and NRP), and the ACTUAL reality is often somewhere between the two. And if we can see both sides it sometimes makes it easier to deal with situation that we find difficult.
I do rather think that "telling him not to bother at all" because he "can?t be arsed" when he is seeing DS every week is a bit
, unless there is much more to this than meets the eye...
OTOH, maybe your ex is a plonker of the highest order who doesn't give a toss...