DrDc is unrelated to the issue here. As another commenter guessed, it's just an optimization to Chromium's graphics pipeline. Chrome has a number of processes that need to execute GPU work. For example, there's the renderer process which actually draws the page content into tiles (we refer to this as "rasterization"). There's at least one renderer process per page because of Site Isolation, but there can be more like in the case of iframes. There's also the Viz process that (among other things) handles the composition of all of the tiles generated by the renderers into the final framebuffer (this is known as the Display Compositor). Each of these processes funnels their GL calls into a separate thread called the GPU main thread which as part of Chromium's security model, is the only thread privileged to interact with the actual system graphics drivers.
The insight behind DrDc is that display compositing is higher priority than rasterization, so having both share work on the GPU main thread is bad for performance. DrDc is a large effort, but at the risk of oversimplifying, it's main purpose is to create a new GPU thread that the display compositor can use exclusively. DrDc is still rolling out on most platforms which may explain why it's disabled on your device, but regardless, it should not help with the video playback issues you're seeing.
The insight behind DrDc is that display compositing is higher priority than rasterization, so having both share work on the GPU main thread is bad for performance. DrDc is a large effort, but at the risk of oversimplifying, it's main purpose is to create a new GPU thread that the display compositor can use exclusively. DrDc is still rolling out on most platforms which may explain why it's disabled on your device, but regardless, it should not help with the video playback issues you're seeing.