Had a post typed up just like this before my browser crashed.
I think a big issue is that Dorsett and Horvat get off the same page when they're in the offensive zone. Horvat would do really well to just dominate and continuously keep the puck down low. Dorsett likes to break the cycle.
Matthias would be great for Horvat, the puck wouldn't go to the net much, but they'd have it down low longer.
Totally agree about Dorsett. Dorsett is more suited to playing with guys like Richardson and Hansen. Horvat needs possession wingers - guys like maybe Burrows and Kassian. I would swap the lines up to look like this:
Sedin - Sedin - Vrbata
Higgins - Bonino - Vey
Burrows - Horvat - Kassian
Dorsett/Matthias - Richardson - Hansen
(Could move Hansen up and Vey out, putting Dorsett in Hansen's spot, as well. Rotate all the guys.)
This line-up really spreads out the defensive forwards to help out Vey and Kassian, and each line has its own strengths.
We know the first line works. The second line has looked good like that. Burrows and Kassian can play to Horvat's strengths. 4th line is an energy line where each player is preferable off the rush and using relentless forechecks.
It may seem counter-intuitive to move Horvat up at this point, but I don't think the minutes are too off. Kassian gets 2nd unit PP, Burrows 1st PP and PK, so they get more minutes than Horvat, who would be good for ~10 on this line. I also really liked Burrows with Horvat, and thought that it helped get Burrows back to his game.
That 4th line could easily eat up some minutes and cause some trouble.