Those are just throwaway gibes, to relieve the monotony of repeating "Greta", "Thunberg", and "Greta Thunberg" over and over again. They're not meant to be particularly witty. Indeed, the lack of wit is in some ways the actual joke.
What you've overlooked, or ignored, is what I consider to be the really good wordsmithing that I put into the term "cargo-cult activism". I think it has a pleasing rhythm, and succinctly describes the phenomenon in question. I doubt there's a better term for it, coined or uncoined.
I'm in favor of sincere effort towards real progress and achievable goals. I'm not in favor of cargo-cult activism and the celebration of cargo-cult activists.
It's simple: I dislike cargo-cult activism.
More cargo-cult thinking. And you also managed to make Greta Tintin Eleonora Ernman Thunberg sound like a cynical attention whore. Even I don't go that far.