There's two reasons why I have trouble believing the leak, and neither of them have anything to do with concrete evidence that contradicts it.
For starters, this leak suggests 5 unique characters (Banjo, Geno, Issac, CKs, and Biker). For those of you who've been counting, we have 5 unique newcomers announced so far. That means that in about a month's time, we'll have to double the number of uniques we currently have.
The second reason why I doubt this leak - and I suppose it's not really a good reason to doubt something - is because it's way too good to be true. Banjo, Geno, and Isaac all mashed together in one Direct, with plenty of other characters revealed in between? I don't believe it.