Jacobs was goalline and short yardage last year, his rookie season. That doesn't mean he's earmarked to only serve in that capacity moving forward. The Giants knew Jacobs could help them improve on their previously woeful short yardage performance. Jacobs didn't contribute beyond that because he was still learning all the other things that go along with being a RB in the league ... blocking assignments, selling a route, etc. If Jacobs goes through another season as strictly a Zach Crockett type then he may in fact be pigeonholed to that role, but considering the Giants have explicitly stated they DON'T see him as a fullback, (which means they'll continue to carry an additional FB on the roster) I think it's safe to consider him as a reserve RB and it's misguided to project him as solely a 3rd an 1 guy. Teams won't dedicate a roster spot for that skill, especially if they have to also carry a FB.
While I like what Ward has shown in short doses I don't think he could carry the load if Tiki got hurt. Jacobs, assuming he knows his assignments, could.