Blimey, this has sparked a lot of thoughts on one of the only subjects I really can go on and on and on about so plenty of disagreement on various things.
I wouldn't call Kraftwerk hip hop, I'd call them electronic music, then krautrock if pressed for an alternative (although their hits, unlike earlier, more experimental work, are all firmly 'electronic music' and you could call a lot of it synthpop). Not sure where they actually sit these days as they play much more dance-influenced versions of their tunes out live (seen them twice in the last 5 years, excellent). But they reached a bigger audience through getting sampled like mad by hip hop artists and their music was absorbed into that scene and many others, so they are absolutely a cornerstone of early hip hop.
I think that NO's influence on acid house is overstated really, they certainly got into the spirit of it but every man, woman and beast and the beast's dog suddenly started using drum machines and synths in the late 70s and I feel like acid house would have happened more or less as it did without them. Someone we'd haven't heard of would have stepped into the breach if they hadn't existed, twas a magical convergence of people, drugs, music and technology and the new sound had to break through into our reality somehow (ha ha) (or is it.... or......... IS....... IT?).
And thinking about the original point, honestly I think there is simply nothing else like the role of the MC in any art form. I don't think there's anything like it in the whole of the English language except perhaps the English language itself. A film is a great analogy because a lot of the better MCs produce incredibly dense and immersive lyrics which on first listening convey a mood and parts of a story and reveal more and more detail, nuance of plot and meaning with repetition, when you're not just trying to keep up.... if you're listening to the right MCs and watching the right films. But yeah, I can't think of any other use of the English language which gives the language itself such a strenuous workout. Brrrrrap!