RGB is a mod, in some cases it damages the original artwork, changes the colors and pixel blurring is lost.
If it was a low budget game or a homebrew it’s possible, at this level that doesn’t happen.
These people work with perfectly calibrated dedicated hardware, and this is the importance of the ‘color profile’, the game designers saw on their monitor exactly the same colors that would be seen on a TV with an original Genesis, plus they had TV and monitors to check the output. Of course, they did not take into account an RGB modification.
In some cases it was a PC with specialized software, in others, and in the beginning it was a special hardware to make ‘pixel arts’.
And one feature of the TVOut shader is very important, the ‘TVOut Composite Enable’ normalizes the colors of the RGB output to what they would look like on a real TV.
This is the same case with CGA, EGA of a PC monitor. Colors changed dramatically whether viewed in RGB or composite. This set has a single video configuration, there were sets that had custom outputs RF, Composite, RGV, etc.