Typically, just one lowers in an a loop of 6 interviews is sufficient to reject. On the other hand, a loop with all "meets" isn't a sufficient either. It needs about 3-4 "raises" to overcome just one "lowers". With two "lowers" the candidate won't even make it to the debrief or worse the loop will be cut-short.
The bar-raiser (it's their job) are expected to specifically look for candidates who raise the bar. Raising the bar == better than 50% of "employees" (not job seekers) at their level. The rationale, when the bar-raiser program was created, was that the collective competency in a corporation should increase as more employees are inducted.
Source: I was a bar-raiser at Amazon; 400+ interviews, 300+ as bar-raiser, conducted hiring boot camp, bar-raiser trainings, trained bar-raisers.