Consider this list as the outdoor track season rankings.
Here are the Diamond League Results, which are objectively scored by results:
https://www.diamondleague.com/fileadmin/IDL_Default/files/documents/2016/MeetDocs/Brussels/DiamondRaceStanding.pdf
Rank Name Nation Points Doha (QAT) 6 MAY Rome (ITA) 2 JUN Birmingham (GBR) 5 JUN Oslo (NOR) 9 JUN Monaco (MON) 15 JUL Lausanne (SUI) 25 AUG Brussels (BEL) 8 SEP
1 KIPROP Asbel KEN - 42 - 10 (1.) 10 (1.) 10 (1.) 1 (6.) 3 (4.) 8 (3.)
2 MANANGOI Elijah Motonei KEN - 28 - 6 (2.) 10 (1.) 6 (2.) 6 (2.)
3 IGUIDER Abdelaati MAR - 21- 6 (2.) 3 (4.) 12 (2.)
4 CHERUIYOT Timothy KEN - 20 - 20 (1.)
5 MAKHLOUFI Taoufik ALG -14 -4 (3.) 4 (3.) 6 (4.)
5 BIWOTT Robert KEN - 14 - 6 (2.) 6 (2.) 2 (6.)
7 GREGSON Ryan AUS - 7 - 4 (3.) 1 (6.) 2 (5.)
8 INGEBRIGTSEN Filip NOR - 4 4 (5.)
8 BIRGEN Bethwell KEN - 4 - 3 (4.) 1 (6.)
10 KIBET Vincent KEN -3 - 3 (4.)
11 GRICE Charlie GBR - 1 - 1 (6.)
Centro scored zero.
You can't give the top ranking to someone who scored zero on the season AND didn't run a top 20 time for the year.
Here are the years were the Olympic 1500m champ was ranked #1 or not in the world for the season:
2016 No - Centro won, Kiprop #1
2012 No - Makhloufi won, Kiplagat #1
2008 No - Kiprop won, Keitany #1
2004 No - El Guerrouj won, Lagat #1
2000 No - Ngeny won, El G #1
1996 Yes - Morceli, Morceli
1992 No - Cacho won, Morceli #1
1988 No - Rono won, Cram #1
1984 No - Coe won, Aouita #1
1980 No - Coe won, Elliot #1
So what is so special about Centro's victory in 3:50 and his yearly best of 3:34 that ranked 21 and was 5 seconds behind the leader that compels people to think he had a better comparable season than all of those Olympic champions that failed to rank #1?