I never found the character switching to be of real value
I've always lowkey disliked the multiple protagonists with character switching in a number of ways. While Franklin, Michael and Trevor are all legends in their own right, I've never felt as connected to them as I felt to Niko, CJ or even Tommy. Having only one character makes them more meaningful as they are your only point of view in the gameworld. It makes it easier to RP as that character, instead of juggling three personalities at once.
The promised benefits from character switching weren't even that advantageous. If I understand correctly, the reasoning behind this design choice was to minimize downtime in missions. If one character needs to do something boring like follow a target or drive across the map, you can switch to another character that might have more interesting things to do. People always complained about boring missions in GTA before, and this was supposed to be a solution. In practice however, I rarely felt compelled to use this feature and I only used it when the game reminded/told me to.
Three protagonists could make for an interesting plot, but the story was never really that amazing. I believe that needing to write a story around three characters is more trouble than it's worth. You just end up with three characters that could be more developed if they were the focus of the story and with the occasional cool crossover moment.
(tl;dr) In short I think that character switching takes away from character meaning and personal roleplay/immersion while not really solving anything. After playing GTA V for many years and completing the story many times, I can conclude for myself that the multiple protagonists made the game worse instead of improving it.
How about you?
Sidenote: I think this will work a lot better in GTA VI. Juggling two people instead of three is way easier, especially because they are intimately involved with each other. I also think that being able to play from either gender is more interesting than just different personalities. Rockstar could take this very far. Imagine playing as Lucia and getting harassed by random people on the street because she's attractive. Point is that gender changes your perspective of the world and your role in it a lot more than personalities do. Same can be said about race actually, that's why Franklin was one of my favorites.