A lot of people mistakenly believe that bias lighting will result in crushed blacks. You won't get black crush with brightness levels set correctly both on the display and on the bias light. Above the zero state, there are many levels of brightness. HDR and 4K both introduce more detail which will absolutely get lost during scenes with specular highlights and a darkened room, just to give one example.
If wide swaths of your display are totally black right now, you are probably already crushing blacks. If you use a PLUGE pattern -- some are available to stream on YouTube --just ensure that they include below black levels as some encoding can crush "illegal" black levels. Here's a reference for bias lighting that includes a PLUGE pattern on the sides. (excuse the music :)) If you can see the bars, you definitely aren't crushing blacks.
Besides the capability of the display, we have the content, which doesn't always go to zero. So the content can also look better in spite of the capabilities of the display (SDR 8-bit content - and that's a lot of it, for example). But to fixate on the darkness when HDR offers so much more, I think shortchanges many of the benefits of OLED.
Hollywood colorists grading on professional OLED monitors use bias lighting too. It's not about picture quality of the display but rather our ABILITY to see that picture quality. It's how (non-prescription) sunglasses can improve our vision when driving our car. Putting aside the fact that it absolutely has ergonomic benefits, it enhances our ability to see the picture. The color appears more vivid and the picture is often sharper. Why sharper? The photopupillary reflex narrows the pupils and just like when we stop down a camera, a greater depth of field falls into focus.
Our home theaters are digital, HDR, 4k, but our eyes are much more refined and sensitive analog/human factors in determining what we see. What looks great to us now in home theater technology ALWAYS inevitably sucks in 10 years when the next technology comes along. Remember when we said we couldn't even see the pixels on 1080p? Remember 1080i? We obviously all know that the picture can get better because it always does, as does our ability to pick it apart.
Joel Silver from ISF likes to say that everyone has opinions about how to set up a TV, but there are defined standards that are accepted internationally. We're all entitled to our preferences too. When I'm working on my computer for non color-critical work, I set my bias lighting much higher than the standards.