That's misleading. You can't use madVR with mpv, but that doesn't mean you can't have high quality scaling and dithering. madVR has NGU, which mpv doesn't have, and it has error-diffusion dithering, which mpv doesn't have, so if you need those, the lack of madVR support could be a deal breaker, but the difference in quality between those algorithms and the ones in mpv is fairly subjective. I feel like all the trendy super-resolution algorithms introduce too many ringing, aliasing and strange watercolour-like artefacts, so I much prefer mpv's EWA Lanczos filter, though if you want, there are a number of super-res algorithms available as mpv user-shaders, including SSimSuperRes and NNEDI3. See:
https://github.com/mpv-player/mpv/wiki/User-Scripts#pixel-sh...mpv supports display calibration and HDR conversion as well. You can load a 3DLUT for display calibration if you want, but for mpv, you would more likely load an ICC profile and have it generate the correct LUT automatically. You can even just let it pick up the ICC profile configured in the operating system. As for HDR, there are a number of built-in tone mapping algorithms: https://mpv.io/manual/master/#options-hdr-tone-mapping