I get that Williams is a 'small' forward but I never really felt that way about him watching him play. I think he could handle the opening exchanges, but it's probably more Fitz' preference than Jack's capability.
Definitely Fitz's preference. What you've got to look at is what works best overall. Not just for that one guy. I agree though that Jack could handle Toby's role if it became necessary.
E.g. I reckon Tommy or Jack
could start games and handle it if the starters are out, but since you've got a plodder in the lineup (Kaufusi) who is going to play the same way no matter what, put Tommy/Jack on at the time you think they could
make the most difference and have Kaufusi play the other role.
A lot of Sharks fans (and probably footy fans in general) get hung up on starter v bench. i.e. "this guy is better than that guy so he should be starting" but that is a massive oversimplification of what the coach actually considers when he puts him team together.