I don't really see the problem with the lack of production. Yeah, it'd be nice if the 3rd line could chip in but he got 11 minutes of ice time in a double OT game. Hard to do much with that. His line is playing a role and playing it well and we're currently 6-0.
No big deal if the 3rd line is ice cold at the moment.
I wouldn't say the third line is ice cold "at the moment." The line can't score, and it's a permanent problem. Kakko can't drive the offense like Lafreniere can, at least not now. It would be a MASSIVE boost to the team if it had a third line that could score and a fourth line that could play more consistent minutes, and with one move we could accomplish that, if Chytil was in fact ready.
Wennburg is a decent enough player but he's the clear upgrade candidate. Cuylle and Kakko are both young players with upside and great defensive and possession play. Wennburg helps enhance that but the line needs to have a threat to put one in the net.
Chytil probably adds the scoring spark without taking away the line's possession edge.
Wennburg helps turn the fourth line into even more of a trustworthy shutdown line.
It's a no-brainer IMO.
Of course all the other check boxes for Chytil have to be complete.