Phil - when the wording for 6.2.1 was discussed at the 18 Sept 2008 BOG meeting, there was no discussion of the lighter weight spinnaker then. Rather it was to clarify when the replacement spinnaker could be used during a race. The intention being that only 1 single spinnaker was to be used during a race (setup, launch, douse, repack, ...) rather than swapping "ready packed" sails. It provides the procedure to allow use of the backup and for notification "as soon as practicable" if the primary spinnaker is damaged.

I concur with your analysis if the lighter weight spinnaker were allowed as a change to 5.12.6.1d. If the rule change for allowing 0.5oz spinnaker does not pass, I think that the proposed 6.2.1 wording is a proper change.