I would agree with you Jake. Splitting the course hasn't shown to be very effective in most of the round robin or semi-final matches.
If I recall, the few times it did work was because one side was favored after a wind shift and the leading boat had picked the wrong side.
So, if it is true that Oracle didn't have the speed to drive up and over NZL, perhaps your right that Spithill should have stayed right on NZL and tried to rattle their cage or force an error.
Dropping off the foil, dipping the windward hull, or any number of smaller tweaks could have cost NZL the lead if USA was sitting right there to capitalize, rather than on the other side of the course.
Heck, seeing the (albeit few) gaffs NZL pulled and how quickly leads changed (against SWE and USA) I think splitting the course just doesn't make as much sense anymore...