I see where you're coming from NFU, but when I listen to SYL, I find that the 'joke' aspect only really takes up less than half the songs. Not the sharpest band lyrically, but it's not all a joke. Some of the talent is put to good use.
Take, for example, a song like 'Skeksis', from 'Alien'. I don't really see how the song is 'joke metal', and Devin's talent, which you have acknowledged, is put to good use with some interesting riffs and cool vocal harmonies.
I can see how songs like 'You Suck' would irritate you, but do you genuinely see nothing more in the band than a joke? If so... fair enough I guess.