You are fucking crap
So... Dio wasn't a big fucking joke to begin with?
Have you seen the original "Holy Diver" music video? I assure you, it'll make you cringe much more than the cover video.
Dio's humour was both self-aware and self-effacing. There's no humility or awareness of any sort involved in this. This is just a bunch of tools having a laugh at the expense of something they'll never understand, like sixth grade boys snickering at David because you can see his wang.
Dio in general is a very mediocre band. They've got maybe 2 or 3 cool songs on each of their albums, with the rest all being boring cookie-cutter songs with sludgy, awkward riffs. The lyrics are usually thoroughly laughable, as is the vocal delivery for the most part.
To me, the only redeeming factor for the band is the existence of some truly ass-kicking, memorable pieces like "Holy Diver", "Rainbow in the Dark", or "We Rock". Even those songs have their flaws - there's just enough awesomeness to them to overlook that.
I wouldn't know to what extent Dio is 'joking on himself' during his songs, but if he is, it's more of a sad joke than a funny one. Especially given the dark, serious musical tone that accompanies pretty much all his songs.