Oceanside wasn't really needed after all the build up
They spent a long time trying to get Oceanside to help in the war against Negan, and they kept refusing, Aaron spent days in the woods nearly dying to get them to agree to join the fight. So its like "Ok all this build up and they're gonna charge in and turn the fight around and help Rick and co defeat Negan when it seems like all hope is lost".
But what they did wasn't really that impactful on the war, ok they showed up at Hilltop and killed a small group of random saviors, a group that Tara and the others probably could have taken care of. I mean they built Oceanside up for nearly 2 seasons just to show up and do that?
I was expecting some Game Of Thrones shit like where the Knights of The Vale charged in and saved John Snow, but no they just appear and threw some fire bottles at random no name saviors and that was it. Had they not showed up Rick's group would have still won the war, them helping changed nothing, them coming to help changed nothing, at best you can say they may have saved Tara, but i find it hard to believe Tara would have been killed by random no named Saviors.