Ryan still had an unfair advantage going into the fight. Did he not? That's cheating regardless of whether Team Haney and the commission allowed the fight to go ahead. He didn't meet his contracted weight and had to pay a hefty fine. Ryan was also penalized by the WBC. Their title wasn't at stake for him. It was only on the line for Haney to defend.
Sometimes contracts also include rehydration clauses. If a fighter is over the limit then they have to pay for it. The show almost always goes on in such cases because none of the parties involved want to cancel the headliner (they trained for 8+ weeks). It would jeopardize the entire event.
It can be an advantage and it can be unfair but when the commission accepts the fight then it stops being unfair, as Haney accepted it, it simply becomes an advantage.
But per the definition of the word “cheating” it isn’t actually cheating.