That yearly ranking Nikkei does is NOT based on actual attendance, it's only counted as concerts x max capacity in arenas, with the stated maximum capacity, not the actual capacity for a concert.
So for EXO they have counted something like
Saitama 5x37,000
Yoyogi 3x14,000
Osaka 3x13,000
Fukuoka 3x12,000
They always do like that. Still, the numbers are exaggerated quite a bit like this for ALL artists in the list, so this list actually still gives a very good idea about how big of a fanbase that the artists have.
(and since there is no way to know EXACTLY how much audience different concerts had, this is kind of an easy and somewhat fair way to do it objectively)