I noticed that in Dolphin 5.0, if I set the fullscreen and/or internal resolution higher than my monitor's native resolution (1080p) via DSR, the game still renders at 1080p (3x native res). The game I tested was Metroid Prime 2 in both DX11 and DX12. My GPU is a 980 Ti, and I didn't experience this issue on older versions of Dolphin or on my previous GPU, which was an R9 280.
One way around this is to use 8x MSAA at 3x native res, instead of rendering at a higher resolution.
One way around this is to use 8x MSAA at 3x native res, instead of rendering at a higher resolution.