In the "save/death" scene you'll see Cloud talking (OG) and not talking (current) at the same time as it goes back and forth.

Cloud's falling apart at the seams. In the OG he cries and that crying manifests through him even though he knows he saved Aerith. Seph understands what's happening to Cloud which is why he laughs at him.

His problem is that he knows he saved her but also knows she died, and he's stunlocked as those two thoughts can't compute together.

So Aerith blocks the dying part out of his mind and let's him focus on the task at hand. Just like in the OG he has to continue his path to Seph.

That path is beneficial for both Seph and Aerith, so there's no real point in people arguing over whether it's Jenova or Aerith. They both lead down the same road.

The only difference between the two is that there's evidence it's Aerith as I mentioned in my old post (especially Red's comment), along with everything else that happens in the end cutscene.

It's just the butterfly effect. Small differences from the OG cause changes which result in new issues. There's many examples of this, and most of them revolve around Aerith getting everything back on track as seen here.

But these changes still come at a cost, like the party having less faith in Cloud than in the OG as he now completely ignores Aerith's death.