I thought they were global and pretty large scale, but I haven’t got any numbers for you and I wouldn’t dream of comparing their size with major world religions.
My assertion, which I admit I didn’t express, is that the distinction between cult and religion is less about size and more about how much members lose personal autonomy and how secretive the organisation is about its beliefs and practices.
That’s the way I see it anyway, otherwise there’s not a lot of point having two different words for it. There are grey areas, sure, but that doesn’t mean that there is no distinction.