TransitMatters reports that while, yes, Blue Line trains now trundle along in less without slow zones, the peak-times trip between Wonderland and Bowdoin still takes longer on average than in February, 2023, before the T announced zillions of slow zones everywhere.
TransitMatters says that's because while the tracks are now in good shape, the Blue Line is still suffering "due to a switch issue, a signal issue, or a more significant ops issue altogether."