I think Thornton was signed for leadership much like Marleau had been, he isn't/never was fast so being able to act as a defensive option seems unlikely. Thornton's greatest value might be on the top 2 lines as a possession option, puck distributer which suits his past but he sure isn't what he was so he won't be superior in any sense. I really don't see why TO signed Thornton but it might work out.
Kerfoot had a crappy year last year but I can remember him from his Colorado days, he's better than what he's shown with the Leafs, I chalk it up to unable to soar with eagles when playing with turkeys.
I don't think Matthews needs Marner to score, he's put up superior numbers with a variety of wingers so I'd like to see TO's first line changed to:
Mikheyev/Mathews/Vesey
TO's 2nd line has JT at center and JT has traditionally been thought to improve whoever he plays with which has been what we've seen since he's been in TO:
Kerfoot/JT/Robertson
I think if TO really wants to play 11 forwards 7 d-men it has to have 3 superior lines , the first 2 lines has potential to be good/dominant, maybe, so ideally TO needs to ice another superior line:
Nylander/Hyman/Marner
Which of those lines would be #1 or #3, depends on the day, the opposition, varying factors but in any event TO's forwards as a whole need to become far more responsible defensively.