The new SSD variant performs on-par with the old drive that WD actually sampled for review, once you exhaust the SLC NAND cache, performance craters from 610MB/s to 390MB/s. The new drive offers just 64 percent of the performance of the old drive.

This has lead to criticism that Western Digital has performed a bait and switch.  It produced a brilliant SSDs, got good reviews and then replaced it with one with bad gubbins.

While there's nothing wrong with selling a slower SSD at a good price, and there's nothing right about abusing the goodwill of reviewers and enthusiasts.

What appears to have got many peoples' goat is that reviewers are the customers and they are not inclined to shut up about it.

“As a reviewer of some 20 years, I do not care at all about the fact that SLC cache performance is identical. While I didn't realize it at the time I wrote up the Crucial bait-and-switch on August 16, I've actually been affected by this problem personally. The 2TB Crucial SSD I purchased for my own video editing work is one of the bait-and-switched units, and it's always had a massive performance problem -- as soon as it empties the SLC cache, it falls to what I'd charitably call hard drive-level performance. Performance can drop as low as 60MB/s via USB3.2 (and ~150MB/s when directly connected via NVMe) and it stays there until the copy task is done”, penned one angry reviewer.