Agree with the walking comments. Don’t think banning walking would improve availability. Getting rid of walking would simply move the advantage away from those willing to commit and lock points into a walk very early and instead give it to people running bots to auto book reservations as soon as window opens (mostly larger commercial renters with IT resources/expertise).
Finding a way to reduce the spec reservation market would probably do a lot more for availability. Maybe capping total annual lead guest changes per membership based on total points. After that, a rebooking would be required for lead guest changes.
I think if you limit lead guest changes you'll just find members leaving themselves as the lead guest for their renters. Some have reported on here that the member they rented from wanted to remain the lead guest on the reservation for a rental, in fact.