It's in bad taste is what it is and a lack of a little bit of respect.
Why didn't this Netflix documentary and memoirs stuff happen whilst Prince Phillip and the queen were still alive? Could it possibly be because now they are both brown bread they can't respond to any accusations?
Most of the abuse Diana got was terrible. Obviously Charles fancying Camilla more than her didn't help but I suppose Charles helping to bring up a child that isn't his whilst keeping a lie intact didn't help matters either.
He clearly waited til they died because they were both so good at protecting their kids from media storms when they were alive. I mean apart from the stuff about Harry's (supposed) father cheating on his mother for their entire marriage, and his uncle being a bit of a nonce.
None of the accusations are about the Queen or Philip, he has just waited until Charles and Wills are a bit more 'on their own' in their defence. Stuff comes out in families all the time after someone dies, so in the same vain as everyone saying 'brothers always fight', skeletons always come out of the closet in families when old timers die, that is nothing new either.
I don't think Harry cares about respecting any of them. His thought process is something like 'Mum killed when he was young, father cheated on her the whole time, probably not even his real father so why respect him, brother followed exactly in their Dad's footsteps, lets just take a hatchet to the whole thing'.
Harry is basically the T1000. He has a lot of very clever PR folk working for him that will have an easier time of things now Liz isn't around, I suspect he won't stop until they 'try' to stop him, and the minute they do that, they're risking the entire institution. He's goading them into a reaction, maybe he won't succeed but he's clearly going to have a bloody good go.
As for 'bad taste', that is a very one-sided view. Wills apparently spent the entire stag do trying to convince Harry not to marry Meghan, is that 'good taste'? I don't think Harry cares what is bad taste/disrespectful anymore. You marry who you wanna marry and your big brother should be keeping his beak out, heir or not.