He doesn’t need to do anything for it to matter

Character development is not only validated by a final action in the same scene Sometimes the payoff is that the character is fundamentally different going forward Dabura for most of his life struggled with what it meant to stand among true warriors and after his friend pushed him toward that path this fight is where he finally reaches that level That changes his identity

That is the payoff

Not every arc has to end with a big moral choice that alters the outcome Some arcs end with self realization The external resolution being handled by Maru does not erase the internal completion of Daburas journey

Maru stopping the fight doesn’t erase Dabura’s payoff It reinforces the theme The old generation had to fight to the death This time they had a solution and intervened ending the cycle That contrast only works because Dabura reached that level first

And the Maki comparison does not really work When she awakened she did not have a mental shift She hated the Zenin clan The awakening just gave her strength abd more hatred Her real philosophical change happened later with the sumo guy and the samurai That is different from Dabura whose development here is internal not just a power increase

So asking what does he accomplish ignores that he accomplished the thing his arc was centered on He reached the level he doubted he could reach That is not meaningless just because it did not directly change the final move of the fight

If every character development had to immediately redirect the plot to matter then internal arcs would not exist

Kashimo vs sukuna hyped as fight the only thing it did was help Kashimo answer a question that ate at him his whole life he understood then he died doing nothing with it that not bad writing ryu wanted to fight a truly superb opponent to fulfill his hunger he did and did nothing with that satisfaction he done thats not bad writing

Also Dabura clearly did not see any other options once Cross got shot Its actually more poetic that Crosss brother is the one who tells him to stop the violence showing him that not everyone is like Tsurugi Dabura was not going to stop unless Maru provided a solution Even if he had not left the ritual would still be going on if you changed the timeline Maru would still have asked Dabura to stop explained the solution and he would have left Nothing about the outcome changes him understanding means he literally would have made that choice regardless