Not quite true. If half the benefit goes to the top 5% of income earners it doesn't necessarily mean the other 50% is evenly spread across the other 95%. It could be spread over the slightly lower 5% so, still not reach "the middle class".
"Scheme " is not necessarily negative and accurately describes what an accountant/tax lawyer figures out for a specific case to save taxes. I don't understand your comment about "the people in question already have a corporation set up, so what is the cost of income splitting?"The cost of income splitting falls on the rest of the public who either have to make up the shortfall in tax revenue or suffer a loss in services.
I agree it is important to know where the data came from but this is the first time I have seen anyone ask this question. Where did the data supporting the hysterical death of small business scenarios painted by the business lobby come from?