>Is it still a cult if it gets big enough?
To draw an analogy, if a street gang gets big enough and controls enough territory, is it a government?
The obvious follow up question is that if these phenomena only differ in size of membership, what makes one "legitimate" and the other not? Is there such a thing as a legitimate government and a legitimate religion, or are they all just another level of street gangs and cults?
For governments anyway we have an answer. Sure at some level the organization of hard force in the form of police is subject to the same practical considerations and constraints as the organization of hard force in the form of a gang, and will thus take a superficially similar form, but a gang does not give you a day in court nor does it set up a system of fair and impartial trials nor does it let you vote on its rules. A gang is fundamentally self serving. It exists for the enrichment of itself at the expense of those outside of it. A democracy, in contrast, directly contradicts the premise "the leader is above the law." So there is such a thing as a "legitimate government".
Existence and uniqueness of "legitimate religion" is left as an exercise for the reader.
(btw Trumpism is absolutely a cult. Just look at it, they had to invent the word "Trumpism" to describe the phenomena because it did not fit any other defined political philosophy and the only constant non-contradictory belief it has is loyalty to Trump himself. Seriously, try defining Trumpism in some way other than "agreeing with what Trump says no matter what." Its impossible. That's a cult.)