Yep. Event the cost difference between WLCSP and BGA or QFN is significant in large quantities. It may be 1/3 of the cost of the whole device.
I don't think there is a huge cost difference between WLCSP and COB, but I imagine board cost is higher for WLCSP.
And most modern device can be programmed in-circuit, so it is not a big deal.