My younger son is 2e but is in special ed due to a developmental disorder, so it's been a bit easier to get accommodations on the book for him. Because of the dysgraphia, he is given more time to do the work, less problems to do, alternate assignments, etc. With all of those in place, he still almost failed 6th grade due to zeros. His are due to forgetting assignments, losing them, etc., but my older son who was not 2e, only gifted, almost failed calculus his senior year due to zeros, because he refused to do the homework after the teacher changed the rule and said it was no longer optional.
I don't have any magic words that will help you make it all better - only that you are doing the right thing by not giving up or buying into the lazy mantra. It isn't lazy; you're right. It could be the depression talking or the giftedness talking or ... but whatever it is, it is keeping him from "just playing the game". What it took for my older son to finally start playing the game is to realize he really could flunk out of college and not be able to do what he wanted with his career. Once that reality hit, he started towing the line and doing work that was "beneath him". It isn't always easy, but if you can find your son's currency, the thing he's willing to barter with you to get more of it, then use it with him. But finding the right currency isn't always easy, is it?
Have you considered pushing for an actual IEP? There are more legal options if you can get one.