First of all, don't compare your case to others'. It won't do you any good, just add to your frustration.
Back when I filed for my AOS in 2016, those who filed with me received their GCs within 3-6 months. At some point, I was the only filer left in my topic who got nothing from USCIS.
Each of my filings (AOS, I-751, N400) ended up taking the longest out of the projected wait time, and I had no RFEs.
So just be patient.
And yes, the country of origin might affect certain USCIS processes. For example, during my original AOS filing, at the infopass appointment I learned that my home country took over half a year to clear my background check which resulted in delay of my interview.