Julius Grey is a left-leaning, NDP supporting, lawyer.   He has successfully won cases which were overturned on appeal, and no doubt lost others outright.  He has expert knowledge, but opinions are subject to interpretation for which he has no monopoly on wisdom.  There are left-wing and right-wing economist experts who don't see eye to eye either.  

He's hardly the authority on this issue.  But he is entitled to his opinion, as is everyone else.