I mean, I dunno, the card seems more stacked than Wrestlemania to me. If it turns out even half well (and it will be sold out at the prices posted and due to Saudi Arabia's "Modernization" partnership with WWE for the next 10 year), it'll be pretty hard to ignore.
They're having a championship rematch with Reigns vs. Lesnar that they announced on TV. They had #1 contender's match on both Raw and Smackdown to set up matches for the show. So in that sense it's absolutely canon.
But they're also having super random matches that makes it seem like it exists in it's own world. The 50 Man Rumble match with seemingly nothing on the line. A random John Cena vs. Triple H match. A SUPER random casket match The Undertaker and Chris Jericho.
So one hand it is a canon, storyline driven event and on the other hand it exists in it's own other world.