What This Means
The problem is not the score on the top sailing. It is the shape of the tier. Nearly all of the inventory is Mexico, with a small Australia tail. There is no cabin diversity, no free play, and very limited practical flexibility. The average sailing length is 5.7 nights, but the small count makes that average less useful than it looks.
Compared with the rest of the release, 400 is the least actionable tier. It has the fewest sailings by a wide margin and the narrowest region spread. If a player is trying to use the certificate for choice rather than just access, this is the tier that gives up the most.
The 600-point tier is only slightly better on count, but it at least starts to open Alaska. That makes 400 the clear bottom of the release.