I wasn't thinking about Leo at all actually. a lot of people have generally complained about Killorn in GDTs and elsewhere this year. also not just here, on twitter and stuff too.
I don't agree completely with your (and others) assertion regarding Leo/Killorn because Leo hasn't really shown chemistry with really anybody this year and he it's not like it's only he and Killorn on the ice, there are other players on the ice with them.
Another point, according to evolving hockey, Leo has spent 585 minutes on the ice at 5v5. 433 of the minutes have been on a line with Killorn and 152 minutes have been on lines without Killorn. The xGF% of the Leo/Killorn lines appears to be 46.9% while lines that have Leo and no Killorn are at 39.4%. Much smaller sample size, but starting to think this Killorn/Leo thing is overblown - or at least it isn't worse than everything else.
Leo hasn't really had extended chemistry with anybody, although Killorn/Leo/Mctavish sticks out has having a much stronger xGF. I think it's interesting that Cronin hasn't been shy to change other lines but that pairing has pretty much been stable throughout the year. Maybe it's because they like it for some analytical reason.