First, filters don't kill anything, of course. They simply remove it. Second, filters and purifiers are only functionally the same in this case if the filter has a pore of 0.2 micron. Many filters are larger.

When using chlorine dioxide, the longest wait time for giardia is 2 hours. 30 minutes is commonly accepted by most to be sufficient. It's crypto that takes up to 4 hours in the worst case. Most don't seem to concern themselves with it, though it is definitely present in the backcountry, mostly near livestock areas.