One other alternative might be to blend the Kylo and Rey fight from TFA in so that we don’t need to have Vader state that’s what’s on his mind, and make it immediately clear why they are located in the place that they are.

So the vision could start with flashes of the TFA fight, and then Kylo would find himself alone in the forest. The stuff with Vader happens, interspersed with the occasional clash from TFA. When Kylo lands the hit on Vader, we also see Rey slashing Kylo’s face. This would explain why he’s unbalanced enough to be thrown back by Vader into the air.

There are a couple problems with this, admittedly. If he’s reliving those moments in the forest, just with Vader in the place of Rey, he wouldn’t have the mask on. Yet, at the same time, we do want his mask on since that is what he reforges after this scene. It might also be confusing to audience to be constantly switching between 3 different realities - the past, present, and visionary.