i kinda agree with you because gamera was supposed to be in "godzilla: king of the monsters" alongside anguirus, baragon, gigan, kamacuras, and kumonga (kong was also going to be in the scene but they decided to scrap him) in the ending scene where all the titans bow down to godzilla (proven by concept art). however, legendary found out they had to pay a separate price for each kaiju regardless of screentime, so they just made new ones.