This is called a catch up patch. They've had every other major patch be a catch up patch since forever.

Top-tier raiders get a couple months with BiS, then equivalent (potentially better, potentially worse, depending on gear slot) gear gets released with a heavy grind requirement to allow people who hadn't cleared, or hadn't cared to clear, to catch up before the next raid tier drops. In this way, new players who just reach max level are never left too far behind to catch up and begin raiding if they care to.

There's a salient argument to be had that Diadem breaks this a bit because you have the potential of every gear slot being better than raid gear just doing that, as opposed to the mix and match of earlier catch up patches--but that's a different discussion than the one you're trying to have, so.