Will a Count vectorizer ever perform (slightly) better than tf-idf?
I would say 1000 documents is a bit less to draw any conclusion about the vectorization technique, Neither an increase in True positive by 1 would matter. As the size of the vocabulary increases, TfidfVectorizer would be better able to differentiate rare words and commonly occurring words while Countvectorizer would still give equal weight to all words which is undesirable. So, TfidfVectorizer will give you better performance than CountVectorizer as the size of the vocabulary increases