There are only 3 wedges who have a 5.0 spin. Max Wedge 52 degree.. The Max Wedge 56 degree, and the Max Wedge 60 degree.
One thing that I have noticed is that with no backspin on the ball, it will still backspin. Once you apply the smallest amount of backspin it draws the ball back a huge amount.
What I think is happening is that the 5.0 backspin on these clubs isn't linear, it's exponential. These 3 clubs are the only ones with a 5.0 backspin, so it's possible that it has escaped your notice.
The other thing of note is that if you put forward spin on the ball with these clubs, it does not register on the greens. Basically it only takes away from the back spin the club normally produces.
All of the +5 backspin wedges are available at level 52, which tells me that they are not used in the upper level game, so it might escape notice.
This is just my opinion, but it seems like the +5 Backspin is doing more backspin that intended.