All DVDs and BDs are 8-bit per channel, in YCbCr 4:2:0, 12-bit total.
Players output min. 8-bit 4:2:2 (16-bit total) or more at 10-bit 4:2:2 (20-bit), or 8-bit 4:4:4 (24-bit), without Deep Color. The last is already twice as much bits as the disc.
With DC, it'll be 30-bit (10-bit PC), 36-bit (12-bit PC) or 48-bit (16-bit PC).
RGB is 24-bit (8-bit PC).
Players may not output accurately in all colorspaces. For this player, 4:2:2, 4:4:4 are perfect and RGB has a small error which is invisible.
So player outputs DC to AVR or TV. AVR or TV may need to convert it back down to 24-bit for internal processing. All TVs display finally as RGB.
Some TVs have more accurate picture when sent one format or another. The Pioneer Kuro does slightly better with RGB than YCbCr.
Most displays are 8-bit or lower, some pro LCDs are '10-bit' (it's a bit more complicated than simple numbers in reality).
Sure, starting from higher bits could be better from the very beginning (film to DI ) but colour banding that is present in the studio master source and hard-coded on the disc as 8-bits cannot be smoothed out with 10 or more bits however many bits you throw at it, simply because the rounding up (the damage) has already been done.