It wasn't a bad idea for V. It was something fresh for the GTA series. Nevertheless i hope we'll only play one character in RDR2.
Gameplay-wise 3 playable protagonists offered some cool moments, that's for sure but the story definitely had its shortcomings because of it. After I finished the game I didn't really care about Michael, Franklin and Trevor. I think it's way easier to feel with (for) a single character. The plot and all the missions revolve around that single person. With 3 characters everything gets split into 3 smaller pieces. And after you finished the game it feels like there should have been "more" for each character. That's at least how I felt after V's story.
3 protagonists are just too much. 2 characters could work better imo. Playing as an outlaw and as a sheriff for example. That could make an interesting plot. Or even a gun-slinging prostitute, haha.