Dracoris

What's weirder than that for me is the Horde allied DKs. Surely Bolvar wouldn't want to help the Horde? Or is it that canonically this all happens post War but pre Sylvanas breaking the helm, and we're all best friends at that point?

I don't think you can see him as Bolvar anymore, death cares not for previous factions, in the end, they all ''serve'' the Lich King

I figure he has retained some level of control if he's allowing new DKs to adventure rather than just having them murder paladins like Arthas did? Admittedly DK lore is one of my weaker points though, I could well be wrong.

And it’s also true that the Lich King has never seen factions like horde/alliance. In Wrath the Ebon Blade was cross-faction, Acherus has always been open to both horde and alliance even when the factions are at war. Bolvar saw the Ebon Blade as useful against the legion too

Will be interesting to see what post-Helm Bolvar thinks about everything. I remember reading he'll be at the head of the Ebon Blade in Shadowlands, which is... a bit odd if he's not going to be Lich King anymore.

Control of the scourge (hence second invasion) but he can still raise people up and wield DK type powers, I don’t think he’s suddenly going to start wanging around judgement and consecration

See, I'm less sure about that. The light abandoned Arthas at every specific point, mid Stratholme. Did it ever abandon Bolvar? I'm... not 100% sure on that.

The light probably abandoned him once he got put on the helm of Domination, though I don't think the light abandons you, but other way around, we've seen the light being used for evil as well, so there isn't really a right or wrong for the Light