What's hilariously stupid is to assume that anyone ever said that. Because nobody here did.
And often it's not about cost-efficiency so much as it is about cinematography. Practical effects require certain setups. Scenes have to be shot a certain way. Things have to be set up in ways that facilitate those effects. That puts a big burden on the creative expression of the film, and since we're no longer in the 1950s we don't have to shoot an entire film/series in a way that allows for practical effects.
CGI is often even the more expensive alternative to some practical effects, but it allows for FAR greater creative freedom because you can do almost anything with it.