When Sukuna loses without being able to use his trump cards, dies from a single scratch and his DE is useless against Muzan - that's a fair match
When Kaneki loses because his body is paralyzed by BS and Muzan moves him to Infinity Caslte where Kaneki can never escape - that's a fair match
When Muzan loses because of the difference in speed, skill, AP and range - that's unfair, the match should be closed