Definitely, mate. That's a great point about blues and purples finding pride in "only the strong survive." I do think the bar should be high before promotion. But that's the point of the systematic program. I've talked to several white belts who trained for three months at other gyms before coming to ours and they had learned almost nothing, except how to get submitted and sometimes injured. Other blue belts have come to our gym from other places with major holes in their technical game. The bar should be technically high, not "I paid my dues" high. Plus, as you say, the clear path keeps people engaged and progressing to further belts.
RE: Four Stripe White Belt: Piecing it All Together - BJJ Training Update, May 2018