Cool... I thought that might be the case, but didn't have the endurance to digest that thread.
I know that link you gave in your first post. In fact, it is my base reference initially for what's worth, even though it's not official it's a good and fairly recent reference. Now I had peculiar questions which are not answered so I decided to bookmark some systems I explored to verify some points and stumbled onto this aberration, triple checked and started wondering.
The short answer is that there appear to be "levels" of terraformability, based on how close the planet currently is to Earth-like conditions. Your planet, with 3576 atmospheres worth of water, has quite a bit of work to do on it to make it Earth-like, so itwould not be as "valuable" to a terraformer looking to make a quick, easy colony.
This I can admit, even with very complicated conditions, but the difference is a factor > 10 for very similar planets.
What are the surface conditions like on the other two terraformable planets (A7 and, presumably, A7a as well)?
Temperature is 1,396K, it could also be the problem as I can imagine it's quite hard to lower that for humans, though A5 is 850K, terraformable too and as worth as A7 (220K). Now you're right that pressure is tremendous compared to others.
Well, as FD keeps the formula secret, I'll take it for granted that sometimes, terraformable planets can be of very low value due to some "scientific/technical reason". Not worth a ticket in the issue tracker, I guess. Thanks for your answer.