There are two major problems with the weekly fractal achievements.
First, there's no way to track which ones you've done. They need checkmarks like the other achievements that require a list of entries. I tried to get to the 12 tier 2 fractal's reward, but at 11 I realized there's no way to know which ones I have left to do.
Second, the requirements are too high for the lower tiers and too low for tier 4. It takes 2 days of doing daily fractals to get the reward for tier 4, but all week for tier 1. Unless you're leveling (which we only do once per account), it isn't going to happen. I think tier 4 should require 8-10 (or more), but the other tiers only 5-6 each (or less).