This is exactly what Apple said in the keynote:
"There is one class of displays, it's commonly called reference monitors. And these do deliver true HDR along with these features(>27 inch screen, wide 10-bit color, precise calibration, HDR). But they're still missing these features(>4K res, retina pixel density, highly functional design, quiet operation) and they're incredibly expensive. This one(Sony) is $43,000.
"So our goal, it was simple. make a display that expertly delivers every feature that pros have asked for.
[lots of marketing fluff]
...It's the only display in the industry that delivers every feature on a pros wishlist, and more.
[more marketing fluff]
...making this the world's best pro display."
So there you go. It doesn't matter if they didn't specifically claim it can replace the $43K Sony. They very specifically positioned XDR as a reference monitor-class display and used the $43k Sony as an example. Then immediately claimed XDR not only compares to monitors in this class but can do even more. But in reality it falls very short of these claims.
And it doesn't matter if XDR is a really good display. Fact is it's the most overpriced worst value display in history. Deal with it.