The main reason why AI is "very weak in their criticism of Western targets" is for a very simple reason - Western societies have far lesser violations of issues AI works against.
The worst offender of the West, US is still far better than most of the third world in terms of due process available and incarceration.
When you make statements like that, and if you want to be accurate, you need to define what terms like "Western targets", "Western societies", and "the West" mean. Does it include Saudi Arabia, Poland, Qatar, Israel and Turkey? Certainly, those countries, although maybe not geographically west, all have decent arguments for being labeled as being in the Western sphere of influence.
And in your comparison, are you factoring in the size of the country?
Finally, you must know the US doesn't rate well in terms of incarceration, which is almost the definition of non-liberty. We (of the US) have the worst per-capita rate.
Regarding Amnesty International, I estimate their official opinion is roughly like that of a European country. It's more or less on the good-guy side, but is overly influenced by the US & UK governments.