I think Kase has looked pretty good in Boston. He's had stretches where his whole line has sort of disappeared but it's hard to blame him alone when that's not unheard of for Debrusk and Krejci. They were awesome in that Carolina series and then kind of disappeared against Tampa, but the same was true of the first and 3rd lines so it's kind of silly to single out Kase.
Lack of production aside, he has absolutely passed the eye test for me. He's creative and likes the puck on his stick. I think he and Krejci do a pretty good job of finding each other on the ice but just need to get the timing down and get the 3rd guy involved more. Getting hurt at this time really sucks because I think it was just a matter of time before that line started clicking, including Kase.
As for people doing the "i told you so" shtick, it's a little annoying that people want to gloat after a guy got hurt by a crosscheck to the face, but whatever. Some people derive more joy from being right on the internet than from seeing this team and its players have success.