The paradigm is different:
Mo Farah is the most suspect and most dirty runner of all the groups you have mentionned:
Look at his international career: Most 5k-10k runners are in their prime between 20-25 years old, that's the time most PB are beaten. They stay competitive after but don't improve.
Mo Farah was a nobody until he reached age 28, in 2011, when he joined Salazar.
Before 2011 and Salazar , his result at world events (olympics, WC, WXC) were
2005 XC long race: 37th
2006 XC cross short race: 40th
2007 5k : 6th place
2007: XC long race: 11th
2008 5k: eliminated in heats before the final
2009 5k : 7th place
2010 XC long race: 20th place
In early 2001 he joined Salasazr at Age 28
2011 5k : gold
2011 10k : silver
2012 5k: gold
2013 10k : gold
2013 5k : gold
2015 5k: gold
2015 10k : gold
2016 5k: gold
2016 10k : gold
2017 5k : silver
2017 10k : gold
Mo Farah is the most suspicious athlete of all time.
Suddenly, after joining a camp where the main coach is banned for doping violations, he turned from a journeyman into a world beater.
It's the Lance Arsmstrong of Athletics.