Linking and merging are two different things. With linking, you have two or more reservations and they link the reservation numbers together so the room assigner is alerted that these separate segments are actually one continuous stay: Res 1 (3 nts) <-> Res 2 (2 nts) <-> Res 3 (2 nts).
With merging, they take the nights from two or more separate reservations and move all of the nights into the first reservation, creating one reservation for the entire stay: Res 1 (3 nts) + Res 2 (2 nts) + Res 3 (2 nts) --> Res 1 (7 nts)
Merging is more complicated because they are editing reservations, not just creating a list of associated reservation numbers, so I can see why it would take longer. Merging is the better option because there is absolutely no way the guest could end up having to move rooms or having to check in and check out multiple times. However, they can only merge reservations if they are all owned by the same
DVC member (and for the same resort, room size and booking category obviously). For reservations made by different members that are all part of the same stay, they cannot merge them, they can only link them.