I see Giles as a poor man's Tippett. He's a ruck who is reasonably competent when pinch hitting in the forward line - as distinct from Tippett who is a forward who is quite competent when playing in the ruck.
As a ruckman, Giles is a considerable upgrade on Jenkins. As a forward, it's probably too close to call - I think Jenkins has the potential to be better in the mid-long term, but they're very evenly matched at the current point in time.
If that means that Giles gets selected ahead of Jenkins, then so be it. The benefit of this selection is that Jacobs gets more (and longer) rest periods, due to having a genuine ruck to support him - hopefully this would result in Jacobs playing out the season, not running out of steam a month before the finals. The downside is that Jenkins doesn't get the development time he needs if he is to improve significantly as a KPP forward.