Drake just had to keep Kendrick dancing, waving his hand and there would be no threat. (that's probably my favorite line, it's amazing how he reduced Drake's hiphop street persona to a wannabe rapper that makes pop music and that's what he should stick to)
As for the A minor joke, surely there's no way that was the first time people heard that joke. It's one of oldest in the books. BUT, I will say it was the first time I heard it from the perspective of the expression "to struck a chord", and not from the literal sense, as in coming from a "musician joke", if that makes sense.
Also, the disses don't have to be creative. Something said on twitter from some rando holds no weight compared to the same thing said by one of the biggest rappers in the world, in a song.
69 god, OV-HOE, its all low hanging... if you're a random on the internet who can say anything behind the computer. Everything hits different when it's someone famous and exposed saying it, and making it so catchy is also a plus.