Postby nweismuller » Mon Feb 13, 2017 9:51 pm
Island planets have 2 units of reef biome, 3 of ocean, and 1 of vents, multiplied by size, by default. Tendao has 3 units of reef, 1.5 of ocean, and 1.6 of vents. Coral planets get 4 units of reef, 1.2 of ocean, and 1 of vents. Phidi have a habitability of of 4 for reef biomes, 3 for ocean, and 0.8 for vents. Orthin have a habitability of 4 for vents, but are inferior for ocean and reefs.
As such- an Island world with only Phidi has a maximum population of (2*4)+(3*3)+(1*0.8)=17.8. Adding Orthin increases that to 21 (increasing vents population from 0.8 to 4). Tendao with only Phidi has a maximum population of (3*4)+(1.5*3)+(1.6*0.8)=12+4.5+0.8+0.48=17.78, or actually very slightly lower than a default Island world. If it has Orthin available, this increases to 16.5+(1.6*4)=22.9, or a notable improvement over default Island worlds. A Coral world with only Phidi has a maximum population of (4*4)+(1.2*3)+(1*0.8)=20.4, significantly better than either an Island or Tendao. With Orthin, this increases to 23.6, still better than Tendao.
Tendao is better than normal islands if and only if you have Orthin to supplement your Phidi, and is inferior to Corals even with a mixed Phidi/Orthin population. Terraforming to Coral is never a downgrade for Tendao and should be allowed. Given that the archetypal Phidi playthrough is not very aggressive, it can hardly be guaranteed to have Orthin to upgrade Tendao.
Tl;dr: math indicates that Tendao is only ever superior to normal islands if you have Orthin as well as Phidi, and is always inferior to Corals; Coral terraforming is therefore always an upgrade for Tendao and should be permitted.