We didn't look specifically into this issue when we did our report, but what I can do is provide a brief summary of the literature that we reviewed.
Our assessment of the literature shows that the preferential taxation for small businesses was introduced on the basis that smaller firms face unique constraints in accessing financing to grow, as well as the cost of compliance with tax and regulatory measures. It's harder to spread those fixed costs across a smaller business.
The evidence has come out recently, so I'll just name a few examples. Mintz and Chen in 2011 noted that the current design of the small business preferential rate, and in particular the gradual phase-out as a company grows, effectively raises the marginal effect of tax rates on investment and growth for these businesses in transition, which could act as a deterrent to growth.
Another study, by Dachis and Lester in 2015 for the C.D. Howe Institute, found evidence that some businesses were essentially clustering around these thresholds, and it wasn't possible to tell whether this was because of reduced investment or not growing or tax planning, but their assessment was that this could be creating a distortion.