If having no control makes you worried then renting points may not be for you.
Services like David's do minimize some of the risk but you are correct in that the DVC owner will always own your reservation and theoretically has the power to cancel your res up until the very last minute. ME &
DDP must be arranged by the owner. Disney will not talk to you about anything conneted to the res & you will have absolutely no recourse with WDW if something goes awry.
Just do your homework & make sure you understand what you are getting yourself into before jumping in to the rental pool simply because it is more cost effective.
ETA: I believe most if not all Grand Villas are held for members & not available to book through CRO. IF Central Res did have availability, I would guess it to be at SSR since they have more GV inventory.