I've looked into the way they've changed accuracy mechanics a bit further.
In PoE, each point of accuracy moved your miss/graze/hit/crit windows one point along a scale of 1-100. If your miss window was 1-16 and your crit window was 91-100, then adding one point of accuracy would change those windows to 1-15 and 90-100.
In Tyranny, the fact that there are hardcoded minimum chances (at least 5% crit chance no matter what, at least 10% graze chance no matter what) means that the 1 = 1 system had to be changed; now every point of accuracy only gives a fraction of a point, and the fractions aren't documented anywhere, not even in the combat log. So +1 accuracy and +2 accuracy can have the exact same listed miss/crit/etc. chances, because the difference between them is too small to be displayed.
Miss and crit chance also rise less sharply than they did in PoE, which diminishes the value of accuracy overall. Where +57 relative accuracy would have given you a whopping 57% crit chance in PoE and completely eliminated misses and grazes, in Tyranny it only gives you 13% crit chance (!), which is just 8% more than the hardcoded minimum. Since grazes are hardcoded at 10% and misses at 5%, you're still more likely to miss or graze than you are to crit with +57 accuracy.
Conversely, even at -44 accuracy you still have a 21% hit chance and only a 27% miss chance. It PoE that would have been a 6% hit chance and a 59% miss chance.
Basically, the value of accuracy has been greatly diminished overall. It's still mildly useful on PotD where you can have low relative accuracy at the start, but otherwise you'll easily find better stats to invest in.
This also means that trash mobs whose stats are way below yours will be more durable in Tyranny's system, because your advantage in accuracy will make less of a difference.