"It's only through their increased effort that the lower half of the income spectrum is able to pay less and less tax in Canada."
That sounds nice, but is wrong.
Top marginal rates on wage earners has gone up to 57% in recent years.
Meanwhile,  small business tax rates have steadily fallen.
The Department of Finance released a report in 2015 outlining the changes in effective tax rates for small businesses between 2000 and 2011.
 http://www.fin.gc.ca/taxexp-depfisc/2013/taxexp1303-eng.asp#toc9
The verdict: taxes paid by small businesses, at both the federal and provincial level, decreased dramatically since 2000: a small business in 2011, with $500,000 in taxable income, paid less than half the combined federal and weighted average provincial[i] corporate income tax it paid just 13 years ago.
So, in addition to major tax cuts, small business also uses "sprinkling" and the ability to pay lower tax rate on "passive" funds.
Morneau is on the right track.