You seem fixated on the fact that Crombie was a Progressive Conservative, but party labels mean little in municipal politics. Despite being a Tory, Crombie was undeniably to the left of both Bill Dennison, the NDP mayor who came before him, and Art Eggleton, the Liberal who came soon after.
While most of Crombie policies are today considered standard, at the time they were radically to the left of the status quo. Every previous mayor had called for expressways, slum clearances, and as many towers as a developer could fit in a neighbourhood. Crombie stopped all that, marking a sharp break with the past. Gay rights is another example. Crombie was a staunch advocate for them in the early 1970s, long before this was widely accepted.
By contrast Miller's changes have been evolutionary, rather than revolutionary. He has pushed the city towards his vision, but slowly and without making dramatic changes.