Not everyone can play top-6 minutes though. There are simply not enough minutes to go around. So the players who aren't going to be playing top-6 - like Seth Jarvis - need to be good enough players that they, with their line, can win ES matchups against the opponent's lower lines, contribute on the penalty kill, and be skilled enough that they can sub up in the lineup if someone gets injured or isn't performing up to snuff. You're thinking of Jarvis as a "role player" on Team Canada, when he's not. He's a good 200 foot winger who can contribute on either wing, on any line, at ES (and the PK) and with limited ice time.
In the estimation of the Canadian management team and coaching staff they presumably felt that Jarvis was better suited to do all of those things than, say, Scheifele.
I think of Jarvis more like a 2002 Simon Gagne than a 1998 Rob Zamuner. Gagne was a winger with similar attributes as Jarvis - a fast, 200-foot player who can complement any of the four lines, kill penalties and contribute offensively.
There is no question that guys like Zamuner ('98), Draper ('06) and Kunitz ('14) were poor picks. Jarvis doesn't fit into that category of player, in my opinio.
