>>53422297>So it could make use of its psychic immunityYou have it backwards. Psychic was immune to ghost in Gen 1, and that was presumably due to a programming error.
There's also what
>>53424306 brought up about them not actually getting any poison attacks. Not even something like Smog which both exists in Gen 1 and would be very reasonable for Gastly to learn.
>>53422391Another thing to consider is that evolutions themselves were linked together retroactively and added partway through development.
You can see evidence in the code where Dragonite was added, and Dratini and Dragonair were put in later alongside other two-stages. Plus Gengar and Gastly showing up far before Haunter to connect them.
I think OP has a slightly better case about Ghost type being more of a gimmick in Gen 1, especially due to the implementation of the Silph Scope, but Dragon doesn't seem as clear cut. It was certainly meant to be rare and powerful, but it doesn't strike me as a gimmick in the same way.
