I am having the same error the Michael Carlin had when trying to pass --base-model as an arg to prodigy train. Recreated @koaning's example and got the same problems Michael did. And this problem was reported again here: Trouble loading `en_core_web_lg` as base model - #2 by Jette16.
Would the dev team please look into what's actually happening instead of relying on this work-around?