What did he do that was so bold other than keep taxes low and come up with transit city, that was a political hot potato in the next election?
I'm happy enough to pick a few bones w/David Miller's time in office, but I think you're on the wrong track w/that assertion:
Miller actually did raise overall taxes, because he introduced the City Vehicle Registration Tax, he introduced the City Land Transfer Tax and he also shifted Garbage off the property tax bill onto its own dedicated fee structure.
Additionally, Miller did do a few relatively substantial things that were good.
Notably, the Ridership Growth Strategy for the TTC which significantly boosted every day service and reduced crowding.
He also bolstered Library hours, and made some other solid investments.
Now, could he have done more? Yes; Should he have done more? Probably; Did he underweight the need for a property tax increase? Yes; and did he pull some dumb stunts like selling the street lights to Toronto Hydro.....? Yup.
But overall, he almost certainly led the most competent administration since Amalgamation up to this point.
Granted, that's not saying much.........but still.