Are there any example of story-driven pokemon designs outside of Onix and Spiritomb? I don't feel like there is but i could be wrong.
Onix was designed to be the first boss and Spiritomb was designed to be the champion's lead.
Unfortunately that may also be the reason why both of them are reall weak, which is a shame considering their cool designs (Steelix really didn't do much to fix Onix)