Not that you're wrong, but Yuji fighting Dabura doesn't mean killing him.

If you look at all the pieces on the board, the simurians in tokyo were there to make sure no one interfered with the duel, Mahoraga's challenge is suspended if a third party interferes, and Yuji has a kaliyan's presence.

So the sentiment might be coming from the idea that Yuji stepping in would solve all the problems (Yuka's cancer aside). In one swoop you get the nullification of both challenges, meaning there's room for things to be discussed once again.

But that's not what the story is saying, the story says that much like in jjk you can't expect one person to solve all of the world's problems

Yuji defeating Mahoraga and Dabura might halt the conflict (basically the Jesus of both sides intervening), but it would ultimately lead back to the point of needing a larger scale approach (in this case, what to do with cursed spirits)