You only need to "rip" the 2-3 stitches that are within the seam allowance where the "corners" of the sections of the block abut.
When you rip out these couple of stitches, you can then lightly twist the sections so the joint on the back of the section can separate and lessen the bulk of seams in the seam allowance.
The graphic below is of a 4 patch, but, the process works the same for a pinwheel.
Keep the pinwheel folded as it would be when just removed from under the needle.
Before pressing, remove those couple of stitches, open the block, and press.
Jan in VA