My theory is that the security process doesn't actually take as long as we think. See EE applicants. There is clearly a priority with EE over paper-based, but how can you explain 6 months or less to get PR? Meanwhile paper-based PNPs wait 15-24 months.
In certain cases an applicant may have to undergo an extensive security process, so yes this is the cause for a very long processing time, breaking the dreadful 2-year mark in several cases.
I've read several timelines where people had no security started stated on their notes and suddenly everything is done and they get PPR and COPR. This might also be the case of officers not updating notes and the system properly. How come some of us January 2018 inland applicants got our MR very early, and others got it later or are still waiting for it? And we are all possibly going to be processed as one single batch and get our PPRs around the same time? Background earlier, later, who knows?
The only thing I can think of, really, is that our applications just sit on a queue, and we all have to wait for backlogs to be cleared out and officers to finally pick up our files from the database. Sometimes, applicants may luck out and have an officer pick up a batch "earlier" than expected. It's clear they work with batches, but every now and then you see a few lucky winners who get their application approved fast.
Most applicants are literally waiting for a quick glance and approval stamp while they put their lives on hold, waiting to make career moves, get married, travel, finance a house, etc.