I went back and watched the source video for the D4 leak again and slowed it down. I think the data is probably real. It's logical that Kurast and Mephisto would be next, and the Church of the Light was founded in Kurast. Possible segue to introducing a new holy class. There's also empty space on the map for Kurast.
I think the leak is definitely fake. The video and the leak came out the same day. I thnk the poster watched the video and wrote the leak using ChatGPT and keywords from the video. I think they added the line about WoW to draw in a larger audience.
There's no mention in the data or video of Nahantu, glaives, or half of what's detailed in the leak. The only data that mentions the Spirtborn class involves wings and flying animations and something about armor thorns. They could be angelic in origin, and thorns damage was a major Paladin/Crusader mechanic for certain builds in D2 and D3.
There are also very few lines regarding the Spiritborn class compared to all the other classes so it may be a placeholder name.