I think you mean 24 bit. 8 bit would only be 256 colors total.

8 bits for each of R G and B. So a grey-scale gradient indeed has only 256 colors available. Any gradient also will have about that many at most.

In most gradients, the transitions in R, G, and B are at different places.

True. Also, in most gradients, the full range of R G and B is not used.

In rgb(50, 60, 70) to rgb(150, 130, 120), there are only 200 total transitions.

In terms of color spaces, SRGB (the typical baseline default RGB of desktop computing) is quite naive and inefficient. Pretty much its only upsides are its conceptual and mathematical simplicity. There are much more efficient color spaces which use dynamic non-linear curves and are based on how the rods and cones in human eyes sense color.

The current hotness for wide color gamuts and High Dynamic Range is ICTCP (https://en.wikipedia.org/wiki/ICtCp) which is conceptually similar to (https://en.wikipedia.org/wiki/LMS_color_space).

The same logic applies to any other color space with 24 total bits of resolution.

True!