The three 'laughable' players have all played sitting midfielder, with McDonald pretty much playing that role 100% of the time - here's his position at the weekend http://www.skysports.com/football/cardiff-vs-wolves/teams/339571
By limiting Jack to only being a sitting midfielder, you are kind of talking yourself out of the argument... as there's no need to bring him in with Brown, Mulgrew, Dorrans, McCarthur, Fletcher all vying for the 2 spots in DM, with many of them also able to play elsewhere on the field. The only way Jack would be worthwhile calling up was if he was a better player than any of them, which he isn't. If he moves to a bigger club and plays against a better standard week in, week out, then yes he'll deserve a call up. Until that happens, he'll struggle to get anywhere near the pitch in a Scotland top.