Well yes, the first ride is free, but then if there is no queue, he has to wait the 20 minutes or whatever the minimum is they put on the card (it varies from park to park, some it's 20, others 45) before he can go on another ride, whereas you can run back in the queue and get a re-ride immediately while he sits on a bench waiting out his no-ride time.
RAP also isn't immediate access, only one RAP user can go on a ride at a time, so often, especially on Smiler, the RAP queue is about 20 minutes, it's not all glory and light.
Legoland have fixed this flaw in their system, I'm quiet surprised the other parks haven't bought this on, or copied Paulton's
Edit: Yes he could cover his wristband up and re-enter the main queue with you, but doing so is a risk, the batcher could remember him and refuse entry, take the wristband or if someone sees the band you get decamped off the ride, they're particularly hot on that on Oblivion, I've seen them pull people already strapped into seats off the ride who have disabled wristbands because they used the main queue (because it was walk on), it's swings and roundabouts, where you might see someone getting perceived priority, you might miss another being refused entry or pulled out their seat because they used the wrong queue, RAP users are put in specific seats/rows because in the event of a breakdown they are the most likely person to panic and need to be evac'd first, so that is why they get the back seat more often than not (or in Oblivions case, the seat near the stairs). On Rita they even go as far as telling you which seat to sit in (RAP left, helper right).