Other than the lower point cost, I agree that with only this mod and vanilla there is little reason to create anything other than terran and water planets.
The reason I included some of the other planet types is in case someone makes a mod where those planet types are beneficial in some way. For example, I think there's one mod where there's a supercomputer structure that gets an income bonus if the planet is cold.
To be fair, all the habitable planet types (cat3 & 4) are more-or-less equal in terms of how "good" they are for putting a colony on.
It's just a little confusing as to why you'd have "transitory" types, but be able to bypass them.
Might I suggest that if possible the transitions between planet types be "gated", so that the progression is more gradual.
So that instead of going straight from barren to terran, it would instead go barren -> desert -> arid -> terran.
The individual stages could then be balanced to maintain the overall cost to whatever level is deemed appropriate. And the stages could have multiple choices to include all the useful planet types.
This would also help with the menu being too cluttered as only one place in this path would potentially have a large number of choices, and this could be reduced by splitting off some types into another path.
Eg: barren -> ice -> tundra/water
This however is entirely your choice, as it would be a non-trivial amount of effort to re-organise this.
With respect to other mods, balancing your own should not do so with the expectation that a player will have the other mod(s).
Every content mod should be 100% standalone when combined with the game it is modding.
(I very rarely use the word "should" as it has certain implications. But yeah, this is kind of a biggie.)