Firs of all (there's no second), I want to say that with English being my foreign language my tolerance for corny things is rather big. As far as music goes that is. So tell me how much do lines that you find corny bother you? Like, in Hopsin's Ill Mind Of Hopsin 4 the line "it sucks so much I get blow jobs from it" is great to me but I assume that you guys don't share the same feelings, which makes me come up with some conclusions as well as questions.
For example, I think that artist don't catch flack with non-English speakers over lines of that proportion and given that most people don't even bother with the lyrical part it's easier for them to appeal to more listeners. Further more, they can come across as better than they actually are and hence "all the whack shit on the radio" garbage. The pros here being, good artist can more easily appeal to more devoted Hip-Hop listeners as well, mainly because wordplay tends to be even worse in other languages (at least in mine) and thus again making them look more amazing than they really are.
However, my ultimate question is should rappers go easy on metaphors, punch-lines and all that? I think they do because it's much easier to go wrong with wordplay attempts and get ridiculed among the "proper" listeners (Em's recovery being the prime example). As far as I am concerned, content and rhyming should be the main goals of MC's lyrics. Good stories and introspective verses are always a worthy listen and people tend to find those more relatable.