Its actually not. Cause that's not all he's better than Kendrick at. Matter fact. Kendrick is great with multi's and is more derivative of Eminem style wise than Cole will ever be. He may actually be better than Cole with multis.
I view them similarly on multis to be honest, which wasn't the case a decade or so ago when I would have said Kendrick was better (in part because he simply did it more).
My general view is that Cole is a better punchline lyricists, Kendrick is the better lyricist in general. Mainly because I think he's simply a better writer and more of an evocative, introspective lyricist which is what I prefer (see; Common, Mos, Nas, etc). Whether rapping from his own perspective or others. To me Cole didn't become solid at that until 4YEO, specifically the title track. A track that is rather similar to Sing About Me but doesn't reach those heights emotionally or lyrically because again, they are different writers.
I do not want people to think I'm shytting on Cole as a rapper. I'm on the record, Cole's last album (Off Seasn) is better than Kendrick's last album (Mr Morale).. My problem is simple: I don't want to hear the brag raps and "I'm the best' shyt from someone who had an opportunity to prove it and p*ssy'd out. I cannot respect that, and I can't really respect this track for the same reason.
My Em comparison is moreso about obsession with technical flows/writing over making great music. You can give Eminem the most simple melody in a beat, or basic beat and he's going to over rap on it every time. There were certainly Kendrick eras where he did that - specifically that post GKMC feature run, when he was doing too much - but he hasn't been on that wave in awhile now. Whereas it's all Cole does on features now. And it sticks out more because he often does it alongside a southern rapper or someone like Tee Grizzley. Cole used to be pretty melodic and really good at following where the beat was going, now he just stomps it out.