Right, I understand your points. But there are already so many SMG's and AR's in the game with varying degrees of separation that I think they'd throw some variety in for all the weapon classes.
But it's true that I am biased. Revolvers have always been my favorite weapons in video games (never fired a gun in real life), so I love to see new iterations of them.
The difference with SMGs an ARs is that there are many sub-roles for them to play. There are high damage, low fire rate guns; high fire rate, low accuracy guns; high accuracy, low fire rate guns; etc.
With pistols, they have just as many options. There are 5 altogether, the same number as ARs or SMGs. The only time you would use a revovler is a when you want a big accurate gun with low ammo capacity and a slow fire rate. If you instead wanted a weaker but faster firing gun you would go semi-auto. If you want a high fire rate but low accuracy gun you would go for a machine pistol.
Point is that a revolver is already a sub-class of pistols. There's only one carbine in the game, the CARB-9.