The history of this probably dates back well before my own time - so undoubtedly some holes are here. Hopefully they can be filled in by other authors. The SA records, however, did a round-robin ordering of the Address resource records, and didn't do much with regard to the particular loads on the target machines. The problem was with SAs was that load was not actually a factor, and TGV's relied on VMS specific facilities to order the records. These were both viewed as drawbacks and not as general solutions.
Information changes frequently.
Multiple addresses should be sent out. Must interact with other RRs appropriately. Must be fast. Five minutes was thought as a normal interval, though changes as fast as every sixty seconds could be imagined. This would allow a reasonable stab at recovery during machine failures.