I think saying only kaiju movies from Japan are “real” kaiju movies is like saying only Chinese martial arts films are “real” martial arts films. It’s a genre. The culture that invented a genre doesn’t have exclusive rights to it. Otherwise, only America could make westerns and only England could make swashbucklers( or Spain, or wherever the swashbuckler started).
I entirely disagree. Non-Japanese monster movies are NOT kaiju films - they are monster movies. The whole point of labeling these films as kaiju pictures is to differentiate them from their Western world counterparts. Japan didn’t invent the giant monster movie, but it made its own sub-genre of it, and that’s the kaiju film. What you’re saying is essentially like calling THE SEARCHERS a spaghetti-western.