I'm going to be succinct.
If we look at Canadians, the estimate from Canada Revenue Agency data is that 20% of Canadians that are in TFSAs are hitting their maximum contribution limit. If we look at it by income distribution, for people at the high end of the income scale, about 32% of high-income earners are hitting the maximum. If you look at Canadians in the $20,000 to $25,000 range, about 17% are hitting that limit.
The Department of Finance is right. It is true that high-income earners are using TFSAs more, and more of them are hitting the maximum than people lower on the income scale. You should not characterize the TFSAs as being solely used as a savings vehicle by high-income earners, because in fact the data shows it's being used by Canadians across the entire income spectrum.