I get what you're saying, but for me that's not the definition of a clean victory.
I see a victory when for example character A kills character B and is able to proceed its existance for the rest of its mortal lifespan.
Lets consider the original Gai vs Gokage example. He may win the battle, but he has lost the match. His death is a consequence of his opponent being stronger than his regular self. In order to beat them, he has to beat himself. Cause and consequence, w/o a battle nobody would've died, its all related and comes down to the battle itself.
Battles aren't limited by a timer, i don't think that was a good example.
For me a battle ends when shots stop being fired and depending on what's left, a winner is determined. If the gates are still damaging Gai and eventually take his life, its nothing more than a stalemate imo.
I hope i made sense ._.
the thing is, guy will still live for a certain amount of time after he beats his opponent, but all he did was decrease his mortal lifespan to however long the gates will last. this was what i meant when i was talking about it being only about the battle. it doesnt matter if the person lives another day or another year or even another ten minutes because we all die eventually, its just that guy chose to use a technique that will grant him power defeat his opponent at the cost of his life, which means that his mortal lifespan was reduced from however long it would have been naturally to however long the gates would last, which is why i added the part about the timer.
since he wont know exactly when his body will expire, he is simply going to try his best to defeat his opponent as quickly as possible, and if he has time leftover before he dies from the effects of the gates, then he had won the match officially. nothing else would matter so long as he survives longer than his opponent, since there are too many variables to consider afterwards that may also cause his death outside of battle or even save his life (ex:it is possible that he could even be resucitated by the full power of tsunades creation rebirth moments after collapsing to the effects of the gate or even succummbed to a disease he never knew he had that ended his life before the gates did.)
In my opinion , you cant say character A is stronger than character B if character A has to resort to a suicide technique. So Gai isn't "stronger" than any opponent he needs 8 gates to beat.
the thing is, the 8 gates allow a person to use their bodys full potential, so technically, if they can beat a person with the 8 gates then they can be considered stronger than their opponent because they couldnt survive them at their strongest.
you might counter and say the same for everypne else, but the matter about the gates is that you have to train tour body to use them, and if you cant use them then you cannot access that power and it cannot be considered as part of your actual full power that you are capable of using.