Liddell would get schooled depending on who he fought. Guys like Rampage and Tom Erikson have had success in K-1. Shit Bob Sapp was a K-1 star who beat their best fighter ever twice, need I say more?
But yeah I agree in most cases Liddell would get smashed in K-1. But don't underestimate his kickboxing skills just because he's sloppy in the octagon. That sloppy style is crafted specifically for MMA and it's effective as he's proven. The dude has legit kickboxing skills, very legit skills actually. Are they on par with people he'd have to fight in K-1? I doubt it, at least not polished enough due to him not competing in kickboxing in forever and changing his striking style to MMA and probably getting too used to it to.