According to the 1986 world rankings list Buckner was 2nd behind Aouita, Hutchins 4th. Hutchins had been a regular top 5 guy for several years, just missing out on the bronze in the 84 Olympics. Ovett destroyed both Buckner and Hutchins with 1 year of training for the 5000m.
https://en.wikipedia.org/wiki/1986_in_athletics_
(track_and_field)#5.2C000_metres
In 87 Buckner was again 2nd :
https://en.wikipedia.org/wiki/1987_in_athletics_
(track_and_field)#5.2C000_metres
In 86 and 87 NOBODY was running under 13:10 except Aouita. Ovett was clearly in the form to run 13:00 in 86 and would have been expected to run faster than that in 87, in fact, he was expected by many (including himself) to break the world record in 87. Unfortunately he caught the flu just before the Europeans in 86 and had to drop out in the heat. That effectively was the start of a dramatic loss of form.
To say that 12 athletes could have beaten Ovett in his 86 Commonwealth form is blatantly false.